COEXTRUDED CROSSLINKED MULTILAYER POLYOLEFIN FOAM STRUCTURES MADE FROM RECYCLED POLYOLEFIN MATERIAL AND METHODS FOR MANUFACTURING THE SAME

Abstract

A physically crosslinked, closed-cell, continuous multilayer foam structure is obtained, comprising at least one layer of coextruded polypropylene / polyethylene foam. The multilayer foam structure is obtained by coextruding a multilayer structure comprising at least one layer of foam composition, irradiating the coextruded structure with ionizing radiation, and continuously foaming the irradiated structure.

Description

COEXTRUDED CROSSLINKED MULTILAYER POLYOLEFIN FOAM STRUCTURES MADE FROM RECYCLED POLYOLEFIN MATERIAL AND METHODS FOR MANUFACTURING THE SAME Cross-reference to related applications This application claims the benefit of U.S. patent application number: 14 / 586,721, filed December 30, 2014, U.S. patent application number: 14 / 586,745, filed December 30, 2014, and U.S. patent application number: 14 / 586,781, filed December 30, 2014, the contents of which are incorporated herein by reference in their entirety. Field of invention The invention relates to multilayer polyolefin foam structures. More particularly, to coextruded crosslinked multilayer polyolefin foam structures. Background of the invention Over the past three decades, manufacturing companies have successfully recycled many types of waste: newspapers, cardboard, aluminum, steel, glass, various plastics, films, foams, and more. However, in the case of plastics, certain types of plastic waste are not easily recycled into new, commercially viable products. One such type of waste is metallized polyolefin. l Lbonn / cznz / e / Yi Metallized polyolefins are common in the food packaging industry as barrier films. For example, metallized polyolefin films are used as potato chip bags, snack bar wrappers, and so on. Other applications of metallized polyolefin films, particularly polypropylene films, include packaging for electronic and medical devices, as well as dielectrics in electronic film capacitors. Another application of metallized polyolefins, particularly polypropylene, is in the metal coatings industry. Decorative chrome (trivalent chromium) metallic coatings of injection-molded polypropylene are commonly found on household and domestic appliances, as well as components of other durable and non-durable goods. Decorative vacuum metallization of molded polypropylene and polyethylene parts and thermoformed sheets, including confectionery trays, is also common. Metallic coatings on polypropylene moldings are not limited to decorative applications. Engineering requirements such as EMI and RFI shielding, electrostatic dissipation, wear resistance, heat resistance, and thermal and chemical barriers sometimes necessitate metallic coatings on polypropylene moldings. Currently, several methods and systems exist for recovering and recycling various films and foams, including films and foams containing metallized polyolefins. Furthermore, as manufacturers continually strive to employ more environmentally friendly techniques in the manufacturing process, the commercial uses of these recycled materials are increasing in demand. However, several problems arise when using recycled material in the manufacturing process. Brief description of the invention Applicants have discovered that using recycled material to create foam structures can cause undesirable surface variations in the foam. These undesirable surface variations can include undesirable surface roughness, undesirable surface softness, undesirable surface firmness, undesirable surface energy, and undesirable surface adhesive compatibility, among others. In certain commercial applications, such as the automotive interior finishing industry, the surface properties of the foam are critical. When used for automotive interior finishing, laminators typically laminate a film, fabric, fiber layer, or leather to the foam. The foam laminate can commonly be thermoformed onto a substrate composed of rigid polypropylene, ABS, or wood fiber.For successful foam laminate and / or thermoformed foam laminate formation, the foam surfaces must be consistent. Surface variations in the foam surfaces can negatively affect the strength and quality of the lamination. An example of undesirable surface features is illustrated in Figures 5A and 5B. The foams in Figures 5A and 5B contain 8% parts per hundred parts of resin (PPHR) shredded (but not cryogenically pulverized) foam blended with polypropylene / polyethylene and crosslinked with recycled manufacturing waste. As shown in Figures 5A-5B, the dark areas and gels can be seen as black recycled foam that has not been fully broken down, dispersed, and otherwise reincorporated into these foam sheets. These areas and gels can cause problems for a laminator bonding a film, fabric, fiber layer, or leather to these foams. Specifically, gel adhesion may be less effective, and the foam may delaminate during a secondary operation such as thermoforming, causing a visible blister-like defect on the film, fabric, fiber layer, or leather. The applicants have discovered coextruded multilayer foam structures that include surface foam layers derived from virgin (non-recycled) polyolefin material and inner foam layers derived from one or more recycled polyolefin materials. Furthermore, these foam structures may include recycled foam layers sandwiched or embedded between two non-recycled foam layers. Consequently, these multilayer foam structures may allow manufacturers to continue using recycled material to create lower-cost, more environmentally friendly products that can perform to the same standards as foam structures made entirely from non-recycled material. Multilayer foam structures and methods for manufacturing and using these structures are described. More specifically, formulations of physically crosslinked, coextruded, continuous multilayer foam structures with a closed-cell morphology are described. These formulations may use recycled polyolefin material and incorporate it into a layer. As cited herein, a structure includes, but is not limited to, layers, films, networks, sheets, or other similar structures. Some methods include forming multilayer structures by co-extruding a foam layer and a film layer onto one side of the foam layer. The foam layer may include polypropylene and / or polyethylene and a chemical blowing agent. The foam layer may also include a crosslinking agent, and the chemical blowing agent may be azodicarbonamide. The film layer may include polypropylene and / or polyethylene. The polypropylene in any layer may have a melt flow rate of 0.1–25 grams per 10 minutes at 230°C. The polyethylene in any layer may have a melt flow rate of 0.1–25 grams per 10 minutes at 190°C. In some applications, these coextruded structures can be irradiated with ionizing radiation. The Lbonn / eznz / e / Yi coextruded structures can be irradiated up to four times separately. The ionizing radiation can be alpha rays, beta rays, gamma rays, or electron beams. Additionally, the ionizing radiation can be an electron beam with an accelerating voltage of 200–1500 kV. The electron beam dosage can be 10–500 kGy. The ionizing radiation can crosslink the coextruded structures to a degree of crosslinking of 20–75%. In some applications, irradiated coextruded structures can also be foamed. The foaming process can be continuous to form foam structures. Foaming may involve heating the irradiated structures with molten salt, radiant heaters, a vertical hot air oven, a horizontal hot air oven, microwave energy, or a combination thereof. Multilayer foam structures can have a density of 20–250 kg / m³ and a thickness of 0.2–50 mm. Furthermore, the foam layer can have an average closed-cell size of 0.05–1.0 mm and an average surface roughness of less than 80 µm. Some embodiments include methods for forming multilayer structures by co-extruding a first foam layer and a second foam layer onto one side of the first foam layer. The first foam layer may include polypropylene and / or polyethylene and a first chemical foaming agent. The second foam layer may include polypropylene and / or polyethylene and a second chemical foaming agent. The polypropylene in either layer may have a melt flow index of 0.1–25 grams for 10 minutes at 230°C. The polyethylene in either layer may have a melt flow index of 0.1–25 grams for 10 minutes at 190°C. The first and / or second foam layers may also include a crosslinking agent. In addition, the first and / or second chemical foaming agent may be azodicarbonamide. In some applications, these coextruded structures can be irradiated with ionizing radiation. The coextruded structures can be irradiated up to four times separately. The ionizing radiation can be alpha rays, beta rays, gamma rays, or electron beams. Additionally, the ionizing radiation can be an electron beam with an accelerating voltage of 200–1500 kV. The electron beam dosage can range from 10 to 500 kGy. The ionizing radiation can crosslink the coextruded structures to a degree of crosslinking of 20–75%. In some applications, irradiated coextruded structures can also be foamed. The foaming process can be continuous to form foam structures. Foaming may involve heating the irradiated structures with molten salt, radiant heaters, a vertical hot air oven, a horizontal hot air oven, microwave energy, or a combination thereof. Multilayer foam structures can have a density of 20–250 kg / m³ and a thickness of 0.2–50 mm. Furthermore, the Lbonn / eznz / e / Yi multilayer foam structure can have an average closed-cell size of 0.05–1.0 mm. Additionally, the first and / or second foam layers can have an average surface roughness of less than 80 µm. Some embodiments include methods for forming multilayer structures by co-extruding a first layer and a second layer onto one side of the first layer. The first layer may include polypropylene and / or polyethylene and a first chemical foaming agent. The second layer may include 5–75% by weight of recycled metallized polyolefin material; 25–95% by weight of polypropylene, polyethylene, or a combination of polypropylene and polyethylene; and a second chemical foaming agent. In addition, a third layer may be co-extruded onto one side of the second layer opposite the first layer. The third layer may comprise polypropylene and / or polyethylene and a third chemical foaming agent. Furthermore, the first and / or third layer may be substantially free of recycled polyolefin material. Additionally, any or all of the first, second, or third layers may include a crosslinking agent.In addition, any or all of the first, second, or third chemical foaming agents may be azodicarbonamide. The polypropylene in any layer may have a melt flow index of 0.1–25 grams for 10 minutes at 230°C. The polyethylene in any layer may have a melt flow index of 0.1–25 grams for 10 minutes at 190°C. Recycled metallized polyolefin material may be small enough to pass through a standard 0.375-inch (9.5 mm) sieve. Additionally, recycled metallized polyolefin material may have had metallic layers with a total thickness of 0.003–100 µm before being recycled. In some applications, these coextruded structures can be irradiated with ionizing radiation. The coextruded structures can be irradiated up to four times separately. The ionizing radiation can be alpha rays, beta rays, gamma rays, or electron beams. Additionally, the ionizing radiation can be an electron beam with an accelerating voltage of 200–1500 kV. The electron beam dosage can range from 10 to 500 kGy. The ionizing radiation can crosslink the coextruded structures to a degree of crosslinking of 20–75%. In some applications, irradiated coextruded structures can also be foamed. The foaming process can be continuous to form foam structures. Foaming may involve heating the irradiated structures with molten salt, radiant heaters, a vertical hot air oven, a horizontal hot air oven, microwave energy, or a combination thereof. Multilayer foam structures can have a density of 20–250 kg / m³ and a thickness of 0.2–50 mm. Furthermore, the average closed cell size of the multilayer foam structure can be 0.05–1.0 mm. Additionally, the first and / or third foam layers can have an average surface roughness of less than 80 µm. Some embodiments include a multilayer foam structure having a first coextruded foam layer comprising polypropylene and / or polyethylene and a second coextruded foam layer on one side of the first foam layer. The second foam layer may include 5–75% by weight of recycled metallized polyolefin material and 25–95% by weight of polypropylene, polyethylene, or a combination of polypropylene and polyethylene. The multilayer foam structure may also include a third coextruded foam layer on one side of the second foam layer opposite the first foam layer. The third layer may include polypropylene and / or polyethylene. The first foam layer and / or the third foam layer may be substantially free of recycled polyolefin material. The polypropylene in any layer may have a melt flow index of 0.1–25 grams for 10 minutes at 230°C. The polyethylene in any layer may have a melt flow index of 0.1-25 grams for 10 minutes at 190°C. Multilayer foam structures can have a density of 20–250 kg / m³ and a thickness of 0.2–50 mm. Furthermore, the average closed-cell size of the multilayer foam structure can be 0.05–1.0 mm. The cross-linking degree of the multilayer foam structure can also be 20–75%. Additionally, the first and / or third foam layers can have an average surface roughness of less than 80 µm. l Lbonn / eznz / e / Yi Furthermore, in some forms the multi-layer foam structure can be split, friction-cut, sheared, heat-cut, laser-cut, plasma-cut, water-jet-cut, die-cut, mechanically cut, or hand-cut to form an article. Some configurations include a laminate comprising a multi-layer foam structure and a laminated layer. The multi-layer foam structure may include a first co-extruded foam layer consisting of polypropylene and / or polyethylene and a second co-extruded foam layer on one side of the first foam layer. The second foam layer may consist of 5–75% by weight of recycled metallized polyolefin material and 25–95% by weight of polypropylene, polyethylene, or a combination of polypropylene and polyethylene. The laminated layer may be on one side of the first foam layer opposite the second foam layer. The laminated layer may be a film, fabric, fiber layer, or leather. The first foam layer may have an average surface roughness of less than 80 µm. The multi-layer foam structure may also include a third co-extruded foam layer on one side of the second foam layer opposite the first foam layer.The third layer may include polypropylene and / or polyethylene. The first and / or third layers may be substantially free of recycled polyolefin material. In addition, the laminate may be further thermoformed onto a substrate such that the substrate is on one side of the third foam layer opposite the second foam layer. Some embodiments include methods for forming multilayer structures by co-extruding a first layer and a second layer onto one side of the first layer. The first layer may include polypropylene and / or polyethylene and a first chemical foaming agent. The second layer may include 5–50% by weight of recycled crosslinked polyolefin foam material; 50–95% by weight of polypropylene, polyethylene, or a combination of polypropylene and polyethylene; and a second chemical foaming agent. In addition, a third layer may be co-extruded onto one side of the second layer opposite the first layer. The third layer may comprise polypropylene and / or polyethylene and a third chemical foaming agent. Furthermore, the first and / or third layer may be substantially free of recycled polyolefin material. Additionally, any or all of the first, second, or third layers may include a crosslinking agent.In addition, any or all of the first, second, or third chemical blowing agents may be azodicarbonamide. The polypropylene in any layer may have a melt flow index of 0.1–25 grams for 10 minutes at 230°C. The polyethylene in any layer may have a melt flow index of 0.1–25 grams for 10 minutes at 190°C. The recycled cross-linked polyolefin foam material can be cryogenically sprayed polyolefin foam material. The cryogenically sprayed polyolefin foam material can be small enough to pass through a 3.5 l Lbonn / eznz / e / Yi mesh of the US standard. In some applications, these coextruded structures can be irradiated with ionizing radiation. The coextruded structures can be irradiated up to four times separately. The ionizing radiation can be alpha rays, beta rays, gamma rays, or electron beams. Additionally, the ionizing radiation can be an electron beam with an accelerating voltage of 200–1500 kV. The electron beam dosage can range from 10 to 500 kGy. The ionizing radiation can crosslink the coextruded structures to a degree of crosslinking of 20–75%. In some applications, irradiated coextruded structures can also be foamed. The foaming process can be continuous to form foam structures. Foaming may involve heating the irradiated structures with molten salt, radiant heaters, a vertical hot air oven, a horizontal hot air oven, microwave energy, or a combination thereof. Multilayer foam structures can have a density of 20–250 kg / m³ and a thickness of 0.2–50 mm. Furthermore, the average closed-cell size of the multilayer foam structure can be 0.05–1.0 mm. Additionally, the first and / or third foam layers can have an average surface roughness of less than 80 µm. Some embodiments include a multilayer foam structure having a first coextruded foam layer that includes polypropylene and / or polyethylene and a second coextruded foam layer on one side of the first foam layer. The second foam layer may include 5–50% by weight of recycled crosslinked polyolefin foam material and 50–95% by weight of polypropylene, polyethylene, or a combination of polypropylene and polyethylene. The multilayer foam structure may also include a third coextruded foam layer on one side of the second foam layer opposite the first foam layer. The third layer may include polypropylene and / or polyethylene. The first foam layer and / or the third foam layer may be substantially free of recycled polyolefin material. The polypropylene in any layer may have a melt flow index of 0.1–25 grams for 10 minutes at 230°C.The polyethylene in any layer may have a melt flow index of 0.1-25 grams for 10 minutes at 190°C. The recycled crosslinked polyolefin foam material may include cryogenically sprayed polyolefin foam material. Multilayer foam structures can have a density of 20–250 kg / m³ and a thickness of 0.2–50 mm. Furthermore, the average closed-cell size of the multilayer foam structure can be 0.05–1.0 mm. The cross-linking degree of the multilayer foam structure can also be 20–75%. Additionally, the first and / or third foam layers can have an average surface roughness of less than 80 µm. Moreover, in some forms, the multilayer foam structure can be slitted, friction-cut, sheared, heat-cut, laser-cut, plasma-cut, waterjet-cut, die-cut, mechanically cut, or hand-cut to form a finished product. Some configurations include a laminate comprising a multi-layer foam structure and a laminated layer. The multi-layer foam structure may include a first co-extruded foam layer comprising polypropylene and / or polyethylene and a second co-extruded foam layer on one side of the first foam layer. The second foam layer may include 5–50% by weight of recycled cross-linked polyolefin foam material and 50–95% by weight of polypropylene, polyethylene, or a combination of polypropylene and polyethylene. The laminated layer may be on one side of the first foam layer opposite the second foam layer. The laminated layer may be a film, fabric, fiber layer, or leather. The first foam layer may have an average surface roughness of less than 80 µm. The recycled cross-linked polyolefin foam material may include cryogenically sprayed polyolefin foam material.The multilayer foam structure may also include a third coextruded foam layer on one side of the second foam layer opposite the first foam layer. The third layer may include polypropylene and / or polyethylene. The first and / or third layers may be substantially free of recycled polyolefin material. Furthermore, the laminate may be additionally thermoformed onto a substrate such that the substrate is on one side of the third foam layer opposite the second foam layer. It is understood that the aspects and embodiments of the invention described herein include aspects and embodiments that are essentially comprised of, or consist of, the components or steps listed herein. For all methods, systems, compositions, and devices described herein, the methods, systems, compositions, and devices may comprise, or consist of, the listed components or steps.When a system, composition, or device is described as consisting essentially of the listed components, the system, composition, or device contains the listed components and may contain other components that do not substantially affect the performance of the system, composition, or device, but also does not contain other components that substantially affect the performance of the system, composition, or device other than the components expressly listed; or does not contain a sufficient concentration or quantity of the additional components to substantially affect the performance of the system, composition, or device.When a method is described as consisting essentially of the enumerated steps, the method contains the enumerated steps and may contain other steps that do not substantially affect the result of the method, but the method does not contain any other steps that substantially affect the result of the method other than the steps expressly enumerated. In disclosure, "substantially free from a specific component, specific composition, specific compound, or specific ingredient" in various forms means that less than approximately 5%, less than approximately 2%, less than approximately 1%, less than approximately 0.5%, less than approximately 0.1%, less than approximately 0.05%, less than approximately 0.025%, or less than approximately 0.01% of the specific component, specific composition, specific compound, or specific ingredient is present by weight. Preferably, "substantially free from a specific component, specific composition, specific compound, or specific ingredient" indicates that less than approximately 1% of the specific component, specific composition, specific compound, or specific ingredient is present by weight. Additional advantages of this invention will be readily apparent to those skilled in the art from the following detailed description. As will be understood, this invention is capable of other and different embodiments, and its details are capable of modification in various obvious respects, all without departing from this invention. Accordingly, the examples and description should be regarded as illustrative in nature and not as restrictive. l Lbonn / eznz / e / Yi Brief description of the drawings Exemplary embodiments of the invention will now be described with reference to the accompanying figures, in which: Figure 1A is a backlit enlarged photograph of the foam from example 1; Figure 1B is a front-lit, unenlarged photograph of the foam from example 1; Figure 1C is a backlit enlarged photograph of example 1 not foamed; Figure 2A is a backlit enlarged photograph of the foam from example 2; Figure 2B is a front-lit, unenlarged photograph of the foam from example 2; Figure 2C is an enlarged, backlit, non-foamed photograph of example 2; Figure 3A is a first enlarged backlit photograph of the foam from example 3; Figure 3B is a second enlarged backlit photograph of the foam from Example 3; Figure 3C is a first, unenlarged photo of the foam from example 3; The 3D figure is a second, unenlarged photo of the foam from example 3; Figure 3E is an enlarged, backlit, non-foamy photograph of example 3; Figure 4A is a backlit enlarged photograph of the Lbonn / eznz / e / Yi foam from Example 4; Figure 4B is a front-lit, unenlarged photograph of the foam from example 4; Figure 4C is an enlarged, backlit, non-foamy photograph of example 4; Figure 5A is a first photo of a foam containing recycled and shredded crosslinked polyolefin foam. Figure 5B is a second photo of a foam containing crosslinked and shredded recycled polyolefin foam. Detailed description of the invention Methods for producing crosslinked, closed-cell, coextruded, multilayer foam structures are described. One or more layers of the multilayer foam structure may be derived from recycled polyolefin material. The methods for producing a crosslinked, closed-cell, coextruded, multilayer foam structure that includes a recycled polyolefin foam layer may include the steps of (a) coextrusion, (b) irradiation, and (c) foaming. Coextrusion is the extrusion of multiple layers of material simultaneously. This type of extrusion uses two or more extruders to supply a constant volumetric throughput of material to an extrusion head (die) that can extrude the materials into the desired shape. In the coextrusion stage, foam compositions can be fed into multiple extruders to form a non-foaming, multi-layered structure. For example, foam composition A can be fed into one extruder, and foam composition B can be fed into a second extruder. The method of feeding ingredients into the extruders can be based on the extruder design and the available material handling equipment. Premixing of the foam composition ingredients can be carried out, if necessary, to facilitate dispersion. A Henshel mixer can be used for such premixing. All ingredients can be premixed and fed through a single port on the extruder. Alternatively, ingredients can be fed individually through separate designated ports for each ingredient.For example, if the crosslinking promoter or any other additive is a liquid, the promoter and / or additives can be added through a feed port (or ports) in the extruder or through a vent opening in the extruder (if equipped with venting) instead of being premixed with solid ingredients. Combinations of premixed and individual ingredient port feeding can also be used. Each extruder can supply a constant amount of each composition into one or more manifolds followed by a laminating die to create a non-foaming, coextruded, multilayer sheet. There are two common methods for coextruding materials: (1) feed-block manifolds; and (2) multiple manifolds within the die. The elements of a feed-block manifold may include: (a) inlet ports for the top, middle, and bottom layers; (b) a streamlined melt laminating area that channels separate flow streams into a laminated melt stream within the feed block; (c) an adapter plate between the feed block and the sheet die; and / or (d) a sheet die (similar to a monolayer die), where the laminated melt stream enters the center of the die and extends along the manifold, flowing out of the die outlet as a distinct multilayer extruded piece.The elements of a multi-collector array may be: (a) similar to a single-layer array, except that there is more than one feed channel; (b) that each melt channel has its own choke bar for flow control; and / or (c) that the melt streams converge within the array near the outlet and emerge as a distinct multi-layer extruded piece. Layer thicknesses can be determined by the design of the manifolds and die. For example, an 80 / 20 feed block manifold can deliver compositions in approximately a 4:1 ratio when the speed and size of each extruder are matched accordingly. This ratio can be altered by changing, for example: (a) the relative extrusion speed between extruders; (b) the relative size of each extruder; and / or (c) the composition (i.e., viscosity) of the individual layers. The overall multilayer sheet thickness can be controlled by the overall die spacing. However, the overall multilayer sheet thickness l Lbonn / eznz / e / Yi can be further adjusted, for example, by tensioning (i.e., stretching) the cast multilayer extruded part and / or flattening the cast multilayer extruded part using a stem. Multilayer structures can include at least two layers made of different compositions. In some embodiments, the multilayer structure includes at least one layer of non-recycled polyolefin and at least one layer of recycled polyolefin. For example, the structure can be an A / B layered structure, an A / B / A layered structure, an A / B / C layered structure, or it can have other multiple layers. In some structures, layer B may include recycled polyolefin material and layer A may include non-recycled polyolefin material. However, both layers A and B, and others, can be made of non-recycled polyolefin material or also of recycled polyolefin material.In addition, multilayer structures may include additional layers such as bonding layers, film layers and / or additional foam layers (including additional recycled and / or non-recycled layers) among others. The foam composition fed into the extruder to form the non-recycled layers may include at least one polypropylene, at least one polyethylene, or a combination thereof. These polypropylenes and / or polyethylenes include the same types described below with respect to recycled metallized polyolefin material.That is, polypropylene includes, without limitation, polypropylene, impact-modified polypropylene, polypropylene-ethylene copolymer, impact-modified polypropylene-ethylene copolymer, metallocene polypropylene, metallocene polypropylene-ethylene copolymer, polypropylene-metallocene olefin block copolymer (with a controlled block sequence), polypropylene-based polyolefin plastomer, polypropylene-based polyolefin elastoplastomer, polypropylene-based polyolefin elastomer, polypropylene-based thermoplastic polyolefin blend, and polypropylene-based thermoplastic elastomeric blend. Furthermore, polypropylenes may be grafted with maleic anhydride.Furthermore, polyethylene includes, but is not limited to, LDPE, LLDPE, VLDPE, VLLDPE, HDPE, polyethylene-propylene copolymer, metallocene polyethylene, metallocene ethylene-propylene copolymer, and polyethylene-metallocene olefin block copolymer (with a controlled block sequence), any of which may contain compatibilizers or grafted copolymers containing acetate and / or ester groups. These polyethylenes may be grafted with maleic anhydride. These polyethylenes may also be copolymers and terpolymers containing acetate and / or ester groups, and may be terpolymer copolymers and ionomers containing acetate and / or ester groups.The foam composition fed into the extruder to form the non-recycled layers may include at least approximately 75% by weight of non-recycled polypropylene, polyethylene, or a combination thereof, preferably at least approximately 90% by weight, more preferably at least approximately 95% by weight, and even more preferably at least approximately 98% by weight. Furthermore, the foam compositions fed into the extruder to form the non-recycled layers may be substantially free of recycled polyolefin material. The foam compositions fed into the extruder to form the non-recycled layers may also be 100% by weight of virgin or non-recycled material. Since a wide range of multi-layer foam articles and laminates can be created with the disclosed foam compositions, a wide range of polypropylenes and polyethylenes can be employed in the foam compositions to meet the various end-use requirements of the structures, articles, and laminates. The foam compositions fed into the extruders to form the recycled layers may include recycled material, including but not limited to recycled polyolefin material, recycled metallized polyolefin material, recycled polyolefin film material, recycled metallized polyolefin film material, recycled polyolefin film material, recycled metallized polyolefin foam material, or combinations thereof. The foam composition fed into the extruder to form the recycled layers may include at least approximately 5% by weight of recycled material, preferably at least approximately 10% by weight, and more preferably at least approximately 15% by weight.Furthermore, these foam compositions fed into the extruders to form the recycled layers may include at least approximately 25% by weight, preferably at least approximately 30% by weight, and more preferably at least approximately 40% by weight of polypropylene, polyethylene, or combinations thereof. When the foam compositions fed into the extruder to form the recycled layers include recycled metallized polyolefin material, the foam composition may include approximately 5 to approximately 75% by weight of recycled metallized polyolefin material, preferably approximately 10 to approximately 70% by weight, and more preferably approximately 20 to approximately 60% by weight. In addition, these recycled metallized polyolefin foam compositions may include approximately 25 to approximately 95% by weight, preferably approximately 30 to approximately 90% by weight, and more preferably approximately 40 to approximately 80% by weight of polypropylene, polyethylene, or combinations thereof. Recycled metallized polyolefin material is available in various forms. Examples include, but are not limited to: pellets, granules, chips, flakes, beads, cylinders, bars, wool, and powder. In some embodiments, recycled metallized polyolefin material can be obtained as homogeneous pellets using the process disclosed in WO 2013057737 l Lbonn / eznz / e / Yi A2, which is incorporated herein by reference in its entirety. In some embodiments, flakes or chips of recycled metallized polyolefin material can be obtained from plastic shredders and crushers commonly used to reduce the size of residual profiles, injection-molded parts, etc. In a third example, powdered metallized polyolefin material can be obtained from commercial spraying and cryogenic spraying equipment. Regardless of shape, it may be preferable for recycled material pieces to be reduced in size to pass through a standard sieve of approximately 0.375 inches (9.5 mm). Recycled pieces that do not pass through a standard sieve of approximately 0.375 inches (9.5 mm) may be difficult to shear sufficiently and mix with other ingredients within the extruder. Therefore, a homogeneous structure cannot be obtained. The primary sources of metallized polyolefins are the metallizing and metal coating industries. These industries employ various techniques to obtain metallized polyolefins, including vacuum metallizing, arc or flame spraying, non-electric coating, or non-electric coating followed by electroplating. The coatings are often not limited to a single metallic layer. Polyolefin coated with multiple layers of various metals deposited using different techniques can also be used in the disclosed invention. l Lbonn / eznz / e / Yi Metallized polyolefins can be obtained by vacuum metallization, arc or flame spraying, non-electric coating, or non-electric coating followed by electroplating. Each technique for obtaining metallized polyolefins is briefly described as follows: In vacuum metallization, a metal is evaporated in a vacuum chamber. The vapor then condenses onto the substrate surface, leaving a thin metallic coating. This deposition process is also commonly known as physical vapor deposition (PVD). In flame spraying, a handheld device is used to spray a metallic coating onto the substrate. The primary force behind the deposition is a combustion flame, fueled by oxygen and gas. The metallic powder is heated and melted. The combustion flame accelerates the mixture and releases it as a spray. Arc spraying is similar to flame spraying, but the power source is different. Instead of relying on a combustion flame, arc spraying derives its energy from an electric arc. Two wires, composed of the metallic coating material and carrying a DC electric current, touch each other at their tips. The energy released when the two wires touch heats and melts the wire, while a stream of gas deposits the molten metal onto the surface of the substrate, creating a metallic coating. In non-electric coating, the plastic surface is etched using an oxidizing solution. The surface becomes extremely susceptible to hydrogen bonding as a result of the oxidizing solution, and this bonding typically increases during coating application. The coating process occurs when the polyolefin component (post-etched) is immersed in a solution containing metal ions, which then bond to the plastic surface as a metallic layer. For the coating (electrolytic coating) to be successful, the polyolefin surface must first be made conductive, which can be achieved through a non-current coating. Once the polyolefin surface is conductive, the substrate is immersed in a solution. The solution contains metal salts, connected to a positive current source (cathode). An anodic conductor (negatively charged) is also placed in the bath, creating an electrical circuit in combination with the positively charged salts. The metal salts are electrically attracted to the substrate, where they form a metallic layer. As this process occurs, the anodic conductor, typically made of the same type of metal as the metal salts, dissolves into the solution and replenishes the source of metal salts, which is depleted during deposition. l Lbonn / eznz / e / Yi The amount of coating that can be deposited by each technique varies. Depending on the end-use requirements, one technique may be preferable to another. However, the metallic coatings deposited by these techniques will range from approximately 0.003 pm for a single layer to 100 pm for a multi-layer coating, preferably from 0.006 pm for a single layer to 75 pm for a multi-layer coating, and more preferably from 0.01 pm to 50 pm for a single layer for a multi-layer coating. The metal content in recycled metallized polyolefins varies from approximately 0.05 to approximately 5% by weight. The most common metallic coating applied to polyolefins is aluminum. Less common coatings include trivalent chromium, nickel, and copper. Even less common coatings include, but are not limited to, tin, hexavalent chromium, gold, silver, and co-deposited metals such as nickel-chromium. Those skilled in the art will appreciate that these metallic coatings are not necessarily pure elemental coatings. For example, nickel may be a nickel-phosphorus or nickel-boron alloy, and copper may be a copper-zinc alloy (brass) or a copper-tin alloy (bronze). Regardless of whether the metal is alloyed or not, the specific metal remains the primary component of the coating. It may be preferred that the metallic coating contain 70–100% of the aforementioned metal, more preferably 80–100% of the aforementioned metal, and even more preferably 85–100% of the aforementioned metal.Those skilled in the technique will also appreciate that the surface of the metallic layers can oxidize, and some of the metals can tarnish. Polypropylene and polyethylene films can be vacuum metallized in the film metallization industry. Therefore, any recycled metallized polyolefin can be expected to contain at least one polypropylene, at least one polyethylene, or a mixture of both. For barrier applications (as opposed to decorative applications), polypropylene and polyethylene films can be coextruded with other barrier layer materials, such as EVOH and PVOH. In these cases, these multilayer films may have adhesive bonding layers to join the EVOH and PVOH to the polypropylene or polyethylene. These bonding layers range from polyolefins with acetate or ester groups to polyethylene ionomers. Similarly, polypropylenes and polyethylenes grafted with maleic anhydride are also used in industry to improve adhesion, not only with adjacent EVOH or PVOH, but also with metallic coatings. In the metal coatings industry, polypropylene is often preferred over polyethylene. However, due to the broader end-use requirements for articles produced in this industry, polypropylenes may be blended with other olefins to meet, for example, softness, impact, and adhesion requirements. Therefore, any recycled metallized polyolefin from this industry can be expected to be a blended polyolefin. Polypropylenes comprising the recycled polyolefin component may contain an elastic or softening component, commonly an ethylene, α-olefin, or rubber component. Therefore, the term polypropylene in this disclosure includes, but is not limited to, polypropylene, impact-modified polypropylene, polypropylene-ethylene copolymer, impact-modified polypropylene-ethylene copolymer, metallocene polypropylene, metallocene polypropylene-ethylene copolymer, metallocene polypropylene-olefin block copolymer (with a controlled block sequence), polypropylene-based polyolefin plastomer, polypropylene-based polyolefin elastomer, polypropylene-based polyolefin elastomer, polypropylene-based thermoplastic polyolefin blend, and polypropylene-based thermoplastic elastomeric blend. A non-limiting example of polypropylene is an isotactic homopolypropylene. Commercially available examples include, but are not limited to, Braskem's FF018F, Total Petrochemicals' 3271, and Conoco's COPYLENE™ CH020. A non-limiting example of an impact-modified polypropylene is a homopolypropylene with ethylene-propylene (EP) copolymer rubber. The rubber may be amorphous or semicrystalline but is not present in sufficient quantities to give the material plastomeric or elastomeric properties. Some non-limiting examples of commercially available impact-modified polypropylene are TI4015F and Lbonn / eznz / e / Yi TI4015F2 from Braskem and Pro-fax® 8623 and Pro-fax® SB786 from LyondelIBasell. Polypropylene-ethylene copolymer is polypropylene with random ethylene units. Some non-limiting examples of commercially available polypropylene-ethylene copolymers are Total Petrochemicals' 6232, 7250FL, and Z9421, and Braskem's TR3020F. Impact-modified polypropylene-ethylene copolymer is polypropylene with random ethylene units and ethylene-propylene (EP) copolymer rubber. The rubber may be amorphous or semicrystalline, but it is not present in sufficient quantities to give the material plastomeric or elastoplastomeric properties. A non-limiting example of a commercially available impact-modified polypropylene-ethylene copolymer is Braskem's PRISMA™ 6910. Metallocene polypropylene is metallocene syndicot homopolypropylene, metallocene atactic homopolypropylene, and metallocene isotactic homopolypropylene. Non-limiting examples of metallocene polypropylene are those commercially available under the trade names METOCENE™ from Lyondell Basell and ACHIEVE™ from ExxonMobil. Metallocene polypropylenes are also commercially available from Total Petrochemicals and include, but are not limited to, grades M3551, M3282MZ, M7672, 1251, 1471, 1571, and 1751. Metallocene polypropylene-ethylene copolymer is a syndiotactic, atactic, and isotactic metallocene polypropylene with random ethylene units. Commercially available examples include, but are not limited to, Lumicene® MR10MX0 and Lumicene® MR60MC2 from Total Petrochemicals and Purell® SM170G from LyondelIBaselL Metallocene polypropylene olefin block copolymer is a polypropylene with alternating hard crystallizing blocks and amorphous soft blocks that are not randomly distributed—that is, with a controlled block sequence. An example of a metallocene polypropylene olefin block copolymer includes, but is not limited to, the INTUNE™ product line from Dow Chemical Company. Polypropylene-based polyolefin plastomers (POPs) and polypropylene-based polyolefin elastoplastomers are both metallocene and non-metallocene propylene-based copolymers with plastomeric and elastoplastomeric properties. Non-limiting examples include those commercially available under the trade names VERSIFY™ (metallocene) from Dow Chemical Company, VISTAMAXX™ (metallocene) from ExxonMobil, and KOATTRO™ (non-metallocene) from Lyondell Basell (a line of plastomeric polymers based on 1-butene—certain grades are 1-butene homopolymer-based materials and others are 1-polypropylene-butene copolymer-based materials). Polypropylene-based polyolefin elastomer (POE) is a metallocene and non-metallocene propylene-based copolymer with elastomeric properties. Non-limiting examples of propylene-based polyolefin elastomers include commercially available polymers such as THERMORUN™ and ZELAS™ (non-metallocene) from Mitsubishi Chemical Corporation, ADFLEX™ and SOFTELL™ (both non-metallocene) from LyondeIBasell, VERSIFY™ (metallocene) from Dow Chemical Company, and VISTAMAXX™ (metallocene) from ExxonMobil. Thermoplastic polyolefin blends based on polypropylene (TPO) are polypropylene, polypropylene-ethylene copolymer, metallocene homopolypropylene, and metallocene polypropylene-ethylene copolymer, containing ethylene-propylene copolymer rubber in sufficiently large quantities to impart the plastomeric, elastoplastomeric, or elastomeric properties of thermoplastic polyolefin blends (TPO). Non-limiting examples of polypropylene-based polyolefin polymers include commercially available polymer blends under the trade names EXCELINK™ from JSR Corporation, THERMORUN™ and ZELAS™ from Mitsubishi Chemical Corporation, FERROFLEX™ and RxLOY™ from Ferro Corporation, and TELCAR™ from Teknor Apex Company. Polypropylene-based thermoplastic elastomer (TPE) blend is polypropylene, polypropylene-ethylene copolymer, metallocene homopolypropylene, and metallocene polypropylene-ethylene copolymer, containing diblock or multiblock thermoplastic rubber modifiers (SEBS, SEPS, SEEPS, SEP, SERC, CEBC, HSB, and the like) in sufficiently large quantities to impart the plastomeric, elastoplastomeric, or elastomeric properties of the thermoplastic elastomer (TPE) blend. Non-limiting examples of polypropylene-based thermoplastic elastomer blend polymers include the commercially available polymer blends under the trade names DYNAFLEX® and VERSAFLEX® from GLS Corporation, MONPRENE® and TEKRON® from Teknor Apex Company, and DURAGRIP® from Advanced Polymers Alloys (a division of Ferro Corporation). All of the above polypropylenes can be grafted with maleic anhydride. Non-limiting examples are ADMER® QF500A and ADMER® QF551A from Mitsui Chemicals. It should be noted that most commercially available anhydride-grafted polypropylenes also contain rubber. The term polyethylene includes, but is not limited to, LDPE, LLDPE, VLDPE, VLLDPE, HDPE, polyethylene-propylene copomer, metallocene polyethylene, metallocene ethylene-propylene copomer, and polyethylene-metallocene olefin block copomer (with a controlled block sequence). Metallocene polyethylene is metallocene-based polyethylene with properties ranging from non-elastic to elastomeric. Non-limiting examples of metallocene polyethylene are commercially available under the trade name l Lbonn / eznz / e / Yi ENGAGE™ from Dow Chemical Company, ENABLE™ and EXCEED™ from ExxonMobil, and EXACT™ from Borealis. VLDPE and VLLDPE are very low-density polyethylene and very linear low-density polyethylene containing an elastic or softening component, commonly o-olefins. Non-limiting examples of VLDPE and VLLDPE are commercially available under the trade name FLEXOMER™ from Dow Chemical Company and specific grades of STAMYLEX® from Borealis. Metallocene polyethylene olefin block copolymer is a polyethylene with alternating hard, crystallizable blocks and soft, amorphous blocks that are not randomly distributed, i.e., with a controlled blocking sequence. Examples of metallocene polyethylene olefin block copolymers include, but are not limited to, the INFUSE™ product line from Dow Chemical Company. All of the above polyethylenes can be grafted with maleic anhydride. Non-limiting commercially available examples include ADMER® NF539A from Mitsui Chemicals, BYNEL® 4104 from DuPont, and OREVAC® 18360 from Arkema. It should be noted that most commercially available anhydride-grafted polyethylenes also contain rubber. These polyethylenes can also be copolymers and terpolymers containing acetate and / or ester groups. Comonomer groups include, but are not limited to, vinyl acetate, methyl acrylate, ethyl acrylate, butyl acrylate, glycidyl methacrylate, and acrylic acid. Non-limiting examples are commercially available under the trade names BYNEL®, ELVAX®, and ELVALOY® from DuPont; EVATANE®, LOTADER®, and LOTRYL® from Arkema; ​​and ESCORENE™, ESCOR™, and OPTEMA™ from ExxonMobil. These polyethylenes can also be terpolymer copolymers and ionomers containing acetate and / or ester groups. A common comonomer group is, but is not limited to, methacrylic acid. Non-limiting examples are commercially available under the trade names SURLYN® from DuPont; IOTEK™ from ExxonMobil; and AMPLIFY™ IO from Dow Chemical Company. The polymer component of recycled polyolefin may also contain EVOH and / or PVOH (PVA). EVOH is a copolymer of ethylene and vinyl alcohol. Non-limiting examples are commercially available under the trade names EVAL™ and EXCEVAL™ from Kuraray and SOARNOL™ from [Company Name]. Nippon Gohsei. PVOH is a polyvinyl alcohol. Non-limiting examples are commercially available under the trade names ELVANOL® from DuPont and POVAL®, MOWIOL®, and MOWIFLEX® from Kuraray. The recycled polyolefin foam material used to form the recycled layers includes, but is not limited to, cryogenically pulverized recycled manufacturing waste, crosslinked foam including polypropylene foams, and blended polypropylene / polyethylene foams. When the foam composition fed into the extruder to form the recycled layers includes recycled polyolefin foam material, the foam compositions may include approximately 5 to approximately 50% by weight of recycled polyolefin foam material, preferably approximately 10 to approximately 45%, and more preferably approximately 15 to approximately 40% by weight.In addition, these foam compositions of recycled polyolefin foam material may include from approximately 50 to approximately 95% by weight, preferably from approximately 55 to approximately 90% by weight, and more preferably from approximately 60 to approximately 85% by weight of polypropylene, polyethylene, or combinations thereof. Cryogenic pulverization (also known as cryogenic milling) is a method that can be used to efficiently reduce heat-sensitive, oxidizable, and / or mill-resistant materials into a fine powder. Crosslinked polyolefin foam is an example of such a material that is not well-suited to milling systems at ambient temperatures. In the cryogenic pulverization process, a cryogenic liquid such as nitrogen or carbon dioxide can be used to cool the material before and / or during milling to help prevent melting and / or achieve brittleness. Cryogenically pulverized crosslinked foams containing manufacturing waste (including polypropylene foams, polyethylene foams, and blended polypropylene / polyethylene foams) are commercially available in various particle sizes and distributions in commercial cryogenic pulverizers. Grinding mills commonly contain a screen near the discharge chute to ensure that the material to be pulverized can be reduced to at least a desired maximum particle size. The grinding screen may be at least US Standard 3.5 mesh, preferably at least US Standard 6 mesh, and more preferably at least US Standard 30 mesh. It may be preferable for pieces of recycled foam material to be reduced in size to pass through at least US Standard 3.5 mesh (5.6 mm opening), preferably at least US Standard 6 mesh (3.35 mm opening), and more preferably at least US Standard 30 mesh (0.600 mm opening). A non-limiting example of foam blended with polypropylene, polyethylene, and polypropylene / polyethylene and crosslinked with finely pulverized recycled manufacturing waste is that produced by Midwest Elastomers, Inc. (Wapakoneta, OH). Such recycled foam from Midwest Elastomers can be pulverized using a U.S. standard 30-mesh screen installed near the discharge chute. Recycled polyolefin foam material may also include foam material that already contains recycled polyolefin material. As such, recycled polyolefin foam material may be newly recycled polyolefin material. For example, recycled polyolefin foam material may already contain metallized polyolefin material and / or crosslinked foams with cryogenically powdered recycled manufacturing residues. In addition, recycled polyolefin foam material may include foams derived from recycled metallized polyolefin material as described in U.S. Application No. 14 / 144,986, which is incorporated herein by reference in its entirety. The foam compositions fed into the extruders to form the various foam layers may include at least one polypropylene having a melt flow index of approximately 0.1 to approximately 25 grams for 10 minutes at 230°C and / or at least one polyethylene having a melt flow index of approximately 0.1 to approximately 25 grams for 10 minutes at 190°C. In some embodiments, the melt flow index of the polypropylenes and / or polyethylenes may preferably be approximately 0.3 to approximately 20 grams for 10 minutes at 230°C and 190°C, respectively, and more preferably approximately 0.5 to approximately 15 grams for 10 minutes at 230°C and 190°C, respectively. The melt flow index (MFI) value for a polymer can be defined and measured according to ASTM D1238 at 230°C for polypropylenes and polypropylene-based materials and at 190°C for polyethylenes and polyethylene-based materials using a 2.16 kg piston for 10 minutes. The test time can be reduced for resins with relatively high melt flow. The MFI provides a measure of a polymer's flow characteristics and is an indication of the molecular weight and processability of a polymeric material. If MFI values ​​are too high, corresponding to low viscosity, extrusion according to this disclosure may not be satisfactorily performed. Problems associated with excessively high MFI values ​​include low pressures during extrusion, difficulty adjusting the thickness profile, uneven cooling profile due to low melt viscosity, low melt strength, machine problems, or a combination thereof. Problems with excessively low MFI values ​​include high pressures during melt processing, sheet quality and profile issues, and higher extrusion temperatures that cause a risk of decomposition and activation of the blowing agent. The MFI ranges mentioned above are also important for foaming processes because they reflect the material's viscosity, and viscosity affects foam formation. While not bound by any single theory, it is believed that there are several reasons why particular MFI values ​​are more effective than others. A material with a lower MFI can improve certain physical properties because the longer molecular chain length creates more energy required for the chains to flow when a tension is applied. Furthermore, the longer the molecular chain (MW), the more crystalline entities the chain can crystallize, thus providing greater strength through intermolecular bonds. However, at an excessively low MFI, the viscosity becomes too high. Conversely, polymers with higher MFI values ​​have shorter chains.Therefore, in a given volume of a material with a higher MFI, there are more chain ends at a microscopic level compared to polymers with a lower MFI. These chain ends can rotate and create free volume due to the space required for such rotation (e.g., the rotation that occurs above the Tg, or glass transition temperature of the polymer). This increases the free volume and allows for easy flow under tensile forces. These polypropylenes and / or polyethylenes with specific MFI values ​​that can be used to form any of the layers of the multilayer foam structure include the same types described above. That is, polypropylene includes, but is not limited to, polypropylene, impact-modified polypropylene, polypropylene-ethylene copolymer, impact-modified polypropylene-ethylene copolymer, metallocene polypropylene, metallocene polypropylene-ethylene copolymer, metallocene polypropylene-olefin block copolymer (with a controlled block sequence), polypropylene-based polyolefin plastomer, polypropylene-based polyolefin elastomer, polypropylene-based polyolefin elastomer, polypropylene-based thermoplastic polyolefin blend, and polypropylene-based thermoplastic elastomeric blend. In addition, the polypropylenes can be grafted with maleic anhydride.Furthermore, polyethylene includes, but is not limited to, LDPE, LLDPE, VLDPE, VLLDPE, HDPE, polyethylene-propylene copolymer, metallocene polyethylene, metallocene ethylene-propylene copolymer, and metallocene polyethylene-olefin block copolymer (with controlled block sequence), any of which may contain compatibilizers or grafted copolymers containing acetate and / or ester groups. As described above, these polyethylenes may be grafted with maleic anhydride. These polyethylenes may also be copolymers and terpolymers containing acetate and / or ester groups, and may be terpolymer copolymers and ionomers containing acetate and / or ester groups. When relatively large or thick metal pieces (relative to the foam cell size) are present in the recycled layer of the multilayer foam structure, undesirable voids and large cells can occur. Therefore, it may be necessary to include polypropylene and / or polyethylene with compatibilizers or grafted copolymers containing acetate and / or ester groups as ingredients to prevent the formation of these undesirable voids and large cells. In addition, the foam compositions fed into the extruder may also contain additional additives compatible with the production of the disclosed multilayer foam structures. Common additives include, but are not limited to, organic peroxides, antioxidants, extrusion processing aids, other lubricants, heat stabilizers, colorants, flame retardants, antistatic agents, nucleating agents, plasticizers, antimicrobials, antifungals, light stabilizers, UV absorbers, antiblocking agents, fillers, deodorants, thickeners, cell size stabilizers, metal deactivators, and combinations thereof. Regardless of how all the ingredients are fed into the extruders, the shear force and mixing within an extruder processing recycled polyolefin material should be sufficient to produce a homogeneous layer (provided the recycled polyolefin material fed to the extruder is homogeneous). A co-rotating twin-screw extruder can provide sufficient shear force and mixing throughout the extruder barrel to extrude a layer with uniform properties. Specific energy is an indicator of how much work is being applied during the extrusion of ingredients and how intense the extrusion process is. Specific energy can be defined as the energy applied to a material being processed by the extruder, normalized to a per-kilogram basis. Specific energy can be quantified in kilowatts of energy applied per kilogram of material fed per hour. Specific energy can be calculated according to the formula: l Lbonn / eznz / e / Yi Specific energy = KW (applied) , -A.' Q advance rate·!^; where bonn / eznz / e / Yi KW (applied) = KW (motor rating) * (% of torque from maximum allowed) * (RPM actually running) * (RPM maximum (extruder capacity) * 0.97 (gearbox efficiency) Specific energy can be used to quantify the amount of shearing and mixing of the ingredients within an extruder. The extruders used for the present invention may be capable of producing a specific energy of at least 0.090 kWh / kg, preferably at least 0.105 kWh / kg, and more preferably at least 0.120 kWh / kg. The extrusion temperature for each layer of the multilayer structures must be at least 10°C below the thermal decomposition start temperature of the chemical foaming agent (i.e., blowing). If the extrusion temperature exceeds the thermal decomposition temperature of the foaming agent, the foaming agent will decompose, resulting in unwanted prefoaming. Foam compositions can include a variety of different chemical foaming agents. Examples of chemical foaming agents include, but are not limited to, azo compounds, hydrazine compounds, carbazides, tetrazoles, nitrous compounds, and carbonates. Furthermore, a chemical foaming agent can be used alone or in any combination. Generally, the amount of chemical foaming agent can be approximately the same in the various layers. For example, if one layer has significantly more PPHR of a chemical foaming agent than another layer (assuming the same chemical foaming agent), then the layer that produces less foaming could hinder the expansion of the more foamy layer. Thus, problems can arise with the multilayer structure rippling, bending, and / or folding over itself when the multilayer structure is heated and foams. A chemical foaming agent that may be used in some embodiments is azodicarbonamide (ADCA). The amount of ADCA in a foam layer composition may be less than or equal to approximately 40% PPHR. Thermal decomposition of ADCA commonly occurs at temperatures between approximately 190 and 230°C. In order to prevent ADCA from thermally decomposing in the extruder, the extrusion temperature may be maintained at or below 190°C. Another chemical foaming agent that may be used in some embodiments is p-toluensulfonylhydrazide (TSH). The amount of TSH in a foam layer composition may be less than or equal to 77% PPHR. Another chemical foaming agent that may be used in some embodiments is p-toluensulfonylsemicarbazide (TSS). The amount of TSS in a foam layer composition can be less than or equal to 63% of PPHR.The amount of chemical blowing agent may depend on the thickness of the non-foamed sheet, the desired foam thickness, the desired foam density, the materials to be extruded, the crosslinking percentage, the type of chemical blowing agent (different blowing agents can generate significantly different amounts of gas), among other factors. However, the amount of blowing agent in each layer should be chosen so that the foaming of each layer is relatively equal. If the difference between the decomposition temperature of the thermally degradable blowing agent and the melting point of the polymer with the highest melting point is significant, then a catalyst can be used to decompose the blowing agent. Examples of catalysts include, but are not limited to, zinc oxide, magnesium oxide, calcium stearate, glycerin, and urea. The lowest temperature limit for extrusion may be that of the polymer with the highest melting point. If the extrusion temperature falls below the melting temperature of the polymer with the highest melting point, undesirable unmelted elements may appear in the structure. After foaming, the extruded layer produced below this lower temperature limit may exhibit uneven thickness, a non-uniform cell structure, cell collapse pockets, and other undesirable characteristics. Extruding a non-foamed multilayer sheet (as described in this application) is different from extruding a foamed multilayer sheet, commonly referred to as extrusion foaming. Extrusion foaming can be performed with a physical foaming agent, a chemical foaming agent, or a combination of both. Examples of physical foaming agents are inorganic and organic gases (e.g., nitrogen, carbon dioxide, pentane, butane, etc.) that can be injected under high pressure directly into the polymer melt. These gases can nucleate and expand as the polyolefin melt exits the extrusion die to create the foamed polymer. Examples of chemical foaming agents (e.g., those described above in the disclosure) are solids that can decompose exothermically or endothermally at a decomposition temperature to produce gases.Common gases generated from chemical blowing agents include nitrogen, carbon dioxide, carbon monoxide, and ammonia, among others. To extrude foam using a chemical blowing agent, the agent is dispersed in the polyolefin melt, and the melt is heated above the blowing agent's decomposition temperature while it remains in the extruder and die. The foamed polymer is then produced as the polyolefin melt exits the extrusion die. Regardless of whether the foaming agent is a physical foaming agent, a chemical foaming agent, or a combination thereof, foaming by conventional extrusion generates polyolefin foam structures with surfaces that are significantly rougher than equivalent foam structures produced by the disclosed method of first coextrusion of a non-foamed multilayer sheet, where foaming occurs after extrusion. The rougher surfaces of extruded foam structures are generally caused by larger cell size when compared to foams produced by the disclosed methods of first coextrusion of a non-foamed multilayer sheet.Although the cell size and size distribution of a foam structure may not be critical in some commercial applications, since surface roughness is a function of cell size, foams with larger cells may be less desirable than foam structures with smaller cells for applications requiring a smooth foam surface. As previously mentioned, the surface profile of foam structures is critical in many applications, and therefore extruded foam structures may not be desirable for these applications. Instead, these applications require a smooth foam structure surface to achieve desired properties such as ease of lamination of a film, fabric, fiber layer, and / or leather; contact percentage during lamination; and visual appeal, among others. A comparison between the surface roughness of an extruded foam sheet and a non-extruded foam sheet produced using the methods described herein can be found in the examples section below.The average surface roughness for the foams produced by the methods described herein may be less than approximately 80 µm, less than approximately 70 µm, less than approximately 50 µm, less than approximately 40 µm, less than approximately 30 µm, less than approximately 25 µm, less than approximately 20 µm, less than approximately 15 µm, and less than approximately 10 µm. The maximum height (height between the highest peak and the deepest valley) of the surface of the foams produced by the methods described herein may be less than approximately 700 µm, less than approximately 600 µm, less than approximately 300 µm, less than approximately 250 µm, less than approximately 200 µm, less than approximately 150 µm, and less than 100 µm. The thickness of a non-foamed coextruded multilayer structure can be from approximately 0.1 to approximately 30 mm, preferably from approximately 0.2 to approximately 25 mm, more preferably from approximately 0.3 to approximately 20 mm, and even more preferably from approximately 0.4 to approximately 15 mm. In addition, the thickness of any individual layer, including both recycled and non-recycled layers, in the non-foamed coextruded multilayer structure can be at least approximately 0.05 mm, preferably at least approximately 0.1 mm, more preferably at least approximately 0.15 mm, and even more preferably at least approximately 0.2 mm. l Lbonn / eznz / e / Yi In configurations where foaming is not intended for certain layers of the multilayer structure (e.g., where one layer is a film or coating layer), the non-foaming layers can be thin and easily foldable upon melting so as not to significantly impede the expansion of the foam layers during the foaming process. Physical properties of the non-foaming layers that may hinder the expansion of the foam layers include, but are not limited to, the thickness, flexibility, melt strength, and crosslinking percentage of the non-foaming layer. Similarly, the thickness, flexibility, melt strength, and crosslinking percentage of the foam layers, as well as the final thickness and density of the foam layers, can also affect whether the non-foaming layers inhibit the expansion of the foam layers. In general, the thickness of the non-foamed layers should preferably be no more than approximately 20% of the thickness of the overall coextruded non-foamed structure. When the thickness of the non-foamed layers exceeds approximately 20% of the thickness of the overall coextruded non-foamed structure, problems may arise with the multilayer structure, such as waviness, buckling, and / or folding over itself when the multilayer structure is heated and foamed. Conversely, the thickness of the non-foamed layers is not limited by how thin they can be relative to the overall coextruded non-foamed multilayer structure. For example, the non-foamed layers can be as thin as approximately 0.1 µm (i.e., the common thickness of a thin bonding layer used in multilayer flexible packaging and barrier films). After the coextruded multilayer structure has been produced by the extruders, it can be irradiated with ionizing radiation at a given exposure to crosslink the composition, thus obtaining an irradiated crosslinked multilayer structure. Ionizing radiation is often unable to produce a sufficient degree of crosslinking on polypropylenes, polypropylene-based materials, some polyethylenes, and some polyethylene-based materials. Therefore, a crosslinking promoter is commonly added to the foam compositions fed into the extruders to promote crosslinking. Polymers crosslinked by ionizing radiation are commonly referred to as physically crosslinked. Physical crosslinking differs from chemical crosslinking. In chemical crosslinking, crosslinks can be generated with crosslinking promoters, but without the use of ionizing radiation. Chemical crosslinking commonly involves the use of peroxides, silanes, or vinylsilane. During peroxide crosslinking processes, crosslinking commonly occurs within the extrusion die. In contrast, for silane and vinylsilane crosslinking processes, crosslinking commonly occurs after extrusion during a secondary operation where the crosslinking of the extruded material can be accelerated with heat and moisture. Regardless of the chemical crosslinking process, chemically crosslinked foam structures commonly exhibit surfaces that are significantly rougher than equivalent foam structures produced using the described physical crosslinking method. The rougher surfaces of chemically crosslinked foam structures are generally caused by larger cell sizes compared to foams produced using the described physical crosslinking methods. Although cell size and size distribution of a foam structure may not be critical in some commercial applications, since surface roughness is a function of cell size, foams with larger cells may be less desirable than foam structures with smaller cells for applications requiring a smooth foam surface. As previously stated, the surface profile of foam structures is critical in many applications, and therefore chemically crosslinked structures are undesirable for these applications. Instead, these applications require a smooth foam structure surface to achieve desired properties such as ease of lamination of a film, fabric, fiber layer, and / or leather; contact percentage during lamination; and visual aesthetics, among others. A comparison between the surface roughness (Lbonn / eznz / e / Yi) of a chemically crosslinked sheet and a physically crosslinked sheet produced using the methods described herein can be found in the examples section below. Examples of ionizing radiation include, but are not limited to, alpha rays, beta rays, gamma rays, and electron beams. Among these, an electron beam with uniform energy is preferable for preparing crosslinked multilayer structures. The exposure time, irradiation frequency, and accelerating voltage following electron beam irradiation can vary widely depending on the desired degree of crosslinking and the thickness of the coextruded multilayer structure. However, the ionizing radiation should generally be in the range of approximately 10 to approximately 500 kGy, preferably approximately 20 to approximately 300 kGy, and most preferably approximately 20 to approximately 200 kGy. If the exposure is too low, cell stability may not be maintained during foaming.If the exposure is too high, the moldability of the resulting multilayer foam structure may be poor. (Moldability can be a desirable property when using the multilayer foam structure in thermoforming applications.) Furthermore, the non-foaming multilayer structure may soften through exothermic heat release upon exposure to electron beam radiation, such that the structure may deform when the exposure is too high. Additionally, the polymeric components may also degrade due to excessive polymer chain cleavage. The non-foaming, coextruded multilayer structure can be irradiated up to four times separately, preferably no more than twice, and preferably only once. If the irradiation frequency exceeds approximately four times, the polymer components may degrade to the point that, when foaming, for example, uniform cells will not be created in the resulting foam layers. When the thickness of the coextruded multilayer structure is greater than approximately 4 mm, it may be preferable to irradiate each primary surface of the multilayer profile with ionized radiation to make the degree of crosslinking of the primary surfaces and internal layers more uniform. Electron beam irradiation offers the advantage that coextruded structures of varying thicknesses can be effectively crosslinked by controlling the electron acceleration voltage. The acceleration voltage is typically in the range of approximately 200 to approximately 1500 kV, preferably approximately 400 to approximately 1200 kV, and more preferably approximately 600 to approximately 1000 kV. If the acceleration voltage is less than approximately 200 kV, the radiation may not reach the inner portion of the coextruded structure. As a result, the cells in the inner portion may be coarse and uneven during foaming. Additionally, an acceleration voltage that is too low for a given thickness profile can cause warping, resulting in pores or tunneling in the multilayer foam structure.On the other hand, if the acceleration voltage is greater than approximately 1500 kV, then the polymers may degrade. Regardless of the type of ionizing radiation selected, crosslinking can be performed in such a way that the composition of the coextruded structure can be crosslinked between approximately 20 and approximately 75%, preferably between approximately 30 and approximately 60%, as measured by the Toray Gel Fractional Percentage Method. According to the Toray Gel Fractional Percentage Method, tetralin solvent is used to dissolve non-crosslinked components in a composition. Essentially, the non-crosslinked material is dissolved in tetralin, and the degree of crosslinking is expressed as the weight percentage of crosslinked material in the entire composition. The apparatus used to determine the percentage of polymer crosslinking includes: 100 mesh (0.0045-inch (0.0114 cm) wire diameter); type 304 stainless steel bags; numbered wires and clamps; a Miyamoto thermostatic oil bath apparatus; an analytical balance; a fume hood; a gas burner; a high-temperature oven; an antistatic gun; and three 3.5-liter wide-mouth stainless steel containers with lids. Reagents and materials used include high-molecular-weight tetralin, solvent, acetone, and silicone oil. Specifically, an empty wire mesh bag is weighed and the weight recorded. For each sample, approximately 100 milligrams ± approximately 5 milligrams of sample are weighed and transferred to the wire mesh bag. The weight of the wire mesh bag and the sample, commonly in the form of foam cuts, is recorded.Each bag is attached to the corresponding wire and clamps. When the solvent temperature reaches 130°C, the assembly (bag and sample) is immersed in the solvent. The samples are shaken up and down approximately 5 or 6 times to loosen any air bubbles and thoroughly wet the samples. The samples are then attached to a shaker and shaken for three (3) hours to allow the solvent to dissolve any foam. The samples are then cooled in a fume hood. The samples are washed by shaking them up and down approximately 7 or 8 times in a primary acetone solution. The samples are washed a second time in a second acetone wash. The washed samples are then washed once more in a third container of fresh acetone, as before. The samples are then hung in a fume hood to evaporate the acetone for approximately 1 to 5 minutes.The samples are then dried in a drying oven for approximately 1 hour at 120°C. The samples are cooled for a minimum of 15 minutes. The wire mesh bag is weighed on an analytical balance and the weight is recorded. The crosslinking can then be calculated using the formula 100*(CA) / (BA), where A = weight of empty wire mesh bag; B = weight of wire bag + foam sample before immersion in tetralin; and C = weight of wire bag + dissolved sample after immersion in tetralin. Suitable crosslinking agents include, but are not limited to, commercially available functional, trifunctional, tetrafunctional, pentafunctional, and high-functionality monomers. Such crosslinking monomers are available in liquid, solid, tablet, and powder forms.Examples include, but are not limited to, acrylates or methacrylates such as 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, tetramethylolmethane triacrylate, 1,9-nonanediol dimethacrylate and 1,10-decanediol dimethacrylate; carboxylic acid allylic esters (such as trimellitic acid trialyl ester, pyromellitic acid trialyl ester and oxalic acid diallyl ester); cyanulic acid or isocyanillic acid allylic ethers such as trialyl cyanurate and trialyl isocyanurate; maleimide compounds such as N-phenylmaleimide and N,N'-m-phenylenebismaleimide; Compounds having at least two tribonds such as italic acid dipropagyl and maleic acid dipropagyl; and divinylbenzene. Additionally, such crosslinking agents may be used alone or in any combination.The amount of crosslinking agent used in a layer composition can vary depending on the molecular weight, functionality, and crosslinking efficiency of the crosslinking agent, as well as the ionizing radiation dose, among other factors. Divinylbenzene (DVB), a difunctional liquid crosslinking monomer, can be used as a crosslinking agent in the present invention and added to an extruder at a level not exceeding approximately 4% PPHR, and preferably from approximately 2% to approximately 3.5% PPHR. Some polymers crosslink more readily than others. Therefore, layers containing polymers more adept at crosslinking may have less crosslinking agent than layers with polymers less adept at crosslinking. In some embodiments, one layer may be intentionally crosslinked more than another layer, which may require the addition of more crosslinking agent to that layer to facilitate further crosslinking. Crosslinks can be generated using a variety of different techniques and can form intermolecularly, between different polymer molecules, and intramolecularly, between portions of a single polymer molecule. Such techniques include, but are not limited to, providing crosslinking agents that are separate from a polymer chain and providing polymer chains that incorporate a crosslinking agent containing a functional group that can form a crosslink or be activated to form a crosslink. After irradiating the extruded structure, foaming can be achieved by heating the crosslinked multilayer structure to a temperature higher than the decomposition temperature of the thermally degradable foaming agent. For the thermally degradable foaming agent azodicardonamide, foaming can be carried out at approximately 200 to approximately 260°C, preferably approximately 220 to approximately 240°C, in a continuous process. A continuous foaming process may be preferable to a batch process for the production of a continuous foam sheet. Foaming can commonly be achieved by heating the cross-linked multilayer structure with molten salt, radiant heaters, a vertical hot air oven, a horizontal hot air oven, microwave energy, or a combination of these methods. Foaming can also be achieved in an impregnation process using, for example, nitrogen in an autoclave, followed by free foaming through molten salt, radial heaters, a vertical hot air oven, a horizontal hot air oven, microwave energy, or a combination of these methods. A preferred combination of molten salt and radiant heaters can be used to heat the cross-linked multilayer structure. Specifically, the side of the irradiated extruded structure not in contact with the molten salt can be heated by radial heaters. Optionally, the cross-linked structure can be softened by preheating before foaming. This can help stabilize the structure's expansion after foaming. The density of the multilayer foam structure can be defined and measured using the cross-sectional or overall density, rather than a core density, as measured by JIS K6767. The multilayer foam structure produced using the method described above can yield foams with a cross-sectional or overall density of approximately 20 to approximately 250 kg / m³, preferably from approximately 30 kg / m³ to approximately 125 kg / m³. The cross-sectional density can be controlled by the amount of blowing agent and the thickness of the coextruded structure. If the structure density is less than approximately 20 kg / m³, the structure may not foam efficiently due to the large amount of chemical blowing agent required to achieve the desired density. Furthermore, if the structure density is less than approximately 20 kg / m³, the expansion of the structure during the foaming stage may become increasingly difficult to control.Furthermore, if the density of the multilayer foam structure is less than 20 kg / m³, then the foam structure may become increasingly prone to cell collapse. Therefore, it can be difficult to produce a multilayer foam structure of uniform density and cross-sectional thickness (with no recycled material) at a density lower than approximately 20 kg / m³. The multi-layer foam structure is not limited to a cross-sectional density of approximately 250 kg / m³. Foams with densities of at least 350 kg / m³, 450 kg / m³, or 550 kg / m³ can also be produced. However, a multi-layer foam structure with a density of less than approximately 250 kg / m³ may be preferable, as higher densities can generally be prohibitively expensive compared to other materials that can be used in a given application. The various foam layers (with or without recycled polyolefin material) in multilayer foam structures can have similar densities. These densities can be determined and adjusted by the amount and type of chemical foaming agents, the thickness of each of the coextruded non-foam layers, and / or the overall thickness of the coextruded non-foam multilayer structure. When the individual foam layers have significantly different densities, problems can arise with the multilayer foam structure, such as rippling, bending, and folding upon itself when heated and foamed. The densities of the foam layers should be within approximately 15% of each other, preferably within approximately 10%, and more preferably within approximately 5%. Multilayer foam structures produced using the method described above may have closed cells. Preferably, at least 90% of the cells have undamaged cell walls, preferably at least 95%, and more preferably more than 98%. The average cell size may be from approximately 0.05 to approximately 1.0 mm, and preferably from approximately 0.1 to approximately 0.7 mm. If the average cell size is less than approximately 0.05 mm, then the density of the multilayer foam structure may commonly be greater than 250 kg / m³. If the average cell size is greater than 1 mm, the foam may have an uneven surface. There is also a possibility that the foam structure may tear undesirably if the cell population in the foam does not have the preferred average cell size. This can occur when the foam structure is stretched or portions of it undergo a secondary process.The cell size in the multilayer foam structure can have a bimodal distribution representing a population of cells in the core of the foam structure that are relatively round and a population of cells in the layer near the surfaces of the foam structure that are relatively flat, thin and / or oblong. The thickness of the multilayer foam structure can range from approximately 0.2 mm to approximately 50 mm, preferably from approximately 0.4 mm to approximately 40 mm, more preferably from approximately 0.6 mm to approximately 30 mm, and even more preferably from approximately 0.8 mm to approximately 20 mm. If the thickness is less than approximately 0.2 mm, foaming may not be effective due to significant gas loss from the primary surfaces. If the thickness is greater than approximately 50 mm, expansion during the foaming stage may become increasingly difficult to control. Therefore, it may become increasingly difficult to produce a multilayer foam structure (with or without recycled polyolefin material) with a uniform density and cross-sectional thickness. The desired thickness can also be achieved through a secondary process such as slitting, roughing, or joining. Slitting, roughing, or joining can produce a thickness range from approximately 0.1 mm to approximately 100 mm. In configurations where foaming of certain layers of the multilayer structure is not proposed, the thickness of the non-foamed layers may be reduced after foaming of the multilayer structure. This can occur because the foaming layers expand and consequently stretch the non-foamed layers. Thus, for example, if the multilayer structure expands to twice its original area, the thickness of the non-foamed layers can be expected to be approximately half. Furthermore, if the multilayer structure expands to four times its original area, the non-foamed layers can be expected to be reduced to approximately one-quarter of their original thickness. The disclosed multi-layer foam structures can be used in a variety of applications. One such application is foam tapes and gaskets. Closed-cell foam tape is commonly used in areas such as window glazing, where strips of foam tape are placed between two panes of glass to seal the air between them. This improves the window's thermal insulation properties. The foam also acts as a cushion for the glass against the effects of thermal expansion and contraction of the building and window frame due to daily and seasonal temperature changes. Similarly, closed-cell foam gaskets are commonly used for sealing and cushioning. Handheld electronic devices and household appliances are two examples that may contain foam gaskets. A soft, flexible foam structure is often suitable as a tape or gasket. When the multilayer foam structure is to be used as a tape or gasket, a pressure-sensitive adhesive layer may be disposed on at least a portion of one or both of the main surfaces. Any pressure-sensitive adhesive known in the art may be used. Examples of such pressure-sensitive adhesives include, but are not limited to, acrylic polymers, polyurethanes, thermoplastic elastomers, block copolymers, polyolefins, silicones, rubber-based adhesives, ethylhexyl acrylate-acrylic acid copolymers, isooctyl acrylate-acrylic acid copolymers, acrylic adhesives, and rubber-based adhesives, as well as combinations thereof. Multilayer foam structures can also be thermoformed. To thermoform a multilayer foam structure, the foam can be heated to the melting point of the polyolefin blend for all layers within the structure. If any layer contains immiscible polymers, the multilayer foam structure may have more than one melting point. In this case, the multilayer foam structure can typically be thermoformed by heating the foam to a temperature between the lowest and highest melting points of the multilayer foam composition. Furthermore, the multilayer foam structure can be thermoformed onto a substrate such as rigid polypropylene, ABS, or wood fiber composite. Preferably, the multilayer foam structure can be thermoformed onto the substrate in such a way that one side of a non-recycled foam layer is applied to the substrate.The substrate itself can also be thermoformed at the same time as the multilayer foam structure. Furthermore, the substrate can be applied to one side (i.e., the surface) of a non-recycled foam layer of the multilayer foam. An example of a thermoformed item is an automotive air duct. A closed-cell foam structure can be particularly suitable for this application due to its lower weight (compared to solid plastic), its insulating properties that help maintain the temperature of the air flowing through the duct, and its resistance to vibration (compared to solid plastic). Thus, a firm, multi-layered foam structure can be suitable for an automotive air duct. In some embodiments, multilayer foam structures are laminates containing the multilayer foam and a laminated layer. Preferably, the laminated layer can be applied to one side (i.e., surface) of a non-recycled foam layer of the multilayer foam. In these laminates, the multilayer foam structure can be combined, for example, with a film and / or foil. Examples of suitable materials for such layers include, but are not limited to, polyvinyl chloride (PVC); thermoplastic polyolefin (TPO); thermoplastic urethane (TPU); fabrics such as polyester, polypropylene, cloth, and other textiles; leather; and / or fiber layers such as nonwovens. Such layers can be manufactured using standard techniques that are well known to those skilled in the art.It is important to note that the multi-layer foam used in the disclosure can be laminated on one or both sides with these materials and may include multiple additional layers. If the multi-layer foam is laminated on both sides, these laminated layers can preferably be applied to the non-recycled foam layers of the multi-layer foam. In these laminates, one layer can be bonded to an adjacent layer by chemical bonds, mechanical means, or combinations thereof. Adjacent laminated layers can also be held together by any other means, including the use of attractive forces between materials with opposite electromagnetic charges or attractive forces between materials that are predominantly hydrophobic or predominantly hydrophilic. In some applications, multi-layer foam structures or laminates are used in automotive interiors such as door panels, door rollers, door inserts, door filler warps, trunk filler warps, armrests, center consoles, seat cushions, seat backs, headrests, rear seat panels, instrument panels, knee pads, or headliners. These multi-layer foam structures or laminates can also be used in furniture (e.g., commercial, office, and residential furniture) such as chair cushions, chair backs, sofa cushions, sofa covers, recliner cushions, recliner covers, bed cushions, mattress cushions, or mattress toppers.These laminates or multi-layer foam structures can also be used in walls as modular walls, movable walls, wall panels, modular panels, office system panels, room dividers, or portable partitions. They can also be used in storage linings (e.g., commercial, office, and residential) that can be mobile or stationary. Furthermore, these laminates and multi-layer foam structures can also be used in coverings such as chair cushion covers, chair back covers, armrest covers, sofa covers, couch cushion covers, recliner cushion covers, recliner covers, bed cushion covers, mattress covers, mattress covers, wall coverings, and architectural coverings. Some options include a first layer of the described multi-layer foam structure and a second layer selected from the group consisting of a solid wood flooring panel, an engineered wood flooring panel, a laminate flooring panel, a vinyl flooring tile, a ceramic flooring tile, a porcelain flooring tile, a stone flooring tile, a quartz flooring tile, a cement flooring tile, and a concrete flooring tile. As indicated above, the second layers can preferably be applied to one side (i.e., to the surface) of the non-recycled layers of the multi-layer foam structure. In these laminates, the first layer can be bonded to the adjacent panel or tile by chemical bonds, mechanical means, or a combination thereof. Adjacent laminated layers can also be bonded to each other by any other means, including the use of attractive forces between materials with opposite electromagnetic charges or attractive forces present between materials that are predominantly hydrophobic or predominantly hydrophilic. A popular method of bonding the described multi-layer foam to a flooring panel—particularly a solid wood flooring panel, a modified wood flooring panel, and a laminate flooring panel—is by means of a pressure-sensitive adhesive layer that can be applied to at least a portion of the foam surface and / or the panel surface. Preferably, the adhesive layer can be applied to the surface of a non-recycled layer of the multi-layer foam structure. Any pressure-sensitive adhesive known in the art can be used. Examples of such pressure-sensitive adhesives include acrylic polymers, polyurethanes, thermoplastic elastomers, block copolymers, polyolefins, silicones, rubber-based adhesives, copolymers of ethyl acrylate and acrylic acid, copolymers of isooctyl acrylate and acrylic acid, mixtures of acrylic and rubber-based adhesives, as well as combinations thereof. Multi-layer foam bonded to the flooring panel—particularly a solid wood flooring panel, a modified wood flooring panel, and a laminate flooring panel—serves several purposes. The foam can reduce the level of reflected sound pressure when the panel is impacted, for example, by walking on the panel in boots or high heels. The foam can also act as a moisture vapor barrier between the panel and the subfloor and can help provide a more uniform deposition between multiple panels, as any unevenness, bumps, or protrusions (e.g., a protruding nail head) in the subfloor will be dampened by the foam. These flooring panels and tiles are commonly installed in residential homes, office buildings, and other commercial buildings. Another embodiment of the present invention provides a paving system comprising: a top floor layer; a base floor layer; and one or more filler layers, wherein at least one of the filler layers contains the described multi-layer foam structure disposed between the base floor layer and the top floor layer. Preferably, the base floor and top floor layers can be applied to the sides / surfaces of non-recycled layers of the multi-layer foam structure. In this system, the foam layer may or may not be bonded to any adjacent layer, including the subfloor or the top floor layer. When any layer is bonded in the described system, the bonding may be achieved through chemical bonds, mechanical means, or a combination thereof. Adjacent layers may also be bonded to each other by any other means, including the use of attractive forces between materials with opposite electromagnetic charges or attractive forces between materials that are predominantly hydrophobic or predominantly hydrophilic. If any of the layers are joined, a popular bonding method is the use of either a one-component urethane adhesive, a two-component urethane adhesive, a one-component acrylic adhesive, or a two-component acrylic adhesive. The adhesive can be applied during system installation in residential homes, office buildings, and commercial buildings. The foam in this system serves several purposes. It can reduce the level of reflected sound pressure when the top layer of the flooring is struck, for example, when walking on the panel in boots or high heels. The foam can also act as a moisture vapor barrier between the panel and the subfloor and help provide a more uniform installation between multiple panels, as any irregularities, bumps, or protrusions (such as a protruding nail head) in the subfloor will be dampened by the foam.For cases where the top floor layer consists of ceramic floor tiles, porcelain floor tiles, stone floor tiles, quartz floor tiles, cement floor tiles, and concrete floor tiles connected by grout and where all layers of the floor system are joined, foam can help reduce grout cracking by dampening variations in thermal expansion and contraction of the various layers of the system. To meet the requirements of any of the above applications l Lbonn / eznz / e / Yi, the structures disclosed in this description may be subjected to various secondary processes, including but not limited to, embossing, corona or plasma treatment, surface roughening, surface smoothing, drilling or micro-drilling, splitting, slicing, grinding, layering, joining, and punching. Examples The following table provides a list of various components and descriptions of those components used in the following examples. Component Description 7250FL Random polypropylene / polyethylene copolymer commercially produced by Total Petrochemicals [MFI is approximately 1.3-1.6 (2.16 kg, 230°C)] 6232 Random polypropylene / polyethylene copolymer commercially produced by Total Petrochemicals [MFI is approximately 1.7-2.3 (2.16 kg, 230°C)] Infuse™ OBC 9107 Polyethylene / octene metallocene block copolymer (with controlled block sequence) commercially produced by Dow [MFI is approximately 0.75-1.25 (2.16 kg, 190°C)] Adflex™ Q100F Reactor-produced thermoplastic polyolefin (rTPO) commercially produced by LyondellBasell [MFI is approximately 0.5-0.7 (2.16 kg, 230°C)] LLP8501.67 linear low density polyethylene (LLDPE) / hexane copolymer commercially produced by ExxonMobil [MFI is approximately 5.9-7.5 (2.16 kg, 190°C)] Component Description ADCA azodicarbonamine TC-181 commercially produced by PT Lauten Otsuka Chemical DVB DVB HP (80% of DVB) commercially produced by Dow PR023 a standard compound antioxidant package from Toray Plastics (America), Inc. for polyolefin foam consisting of 14% antioxidants, 0.35% calcium stearate and 85.65% low-density polyethylene (LDPE) carrier resin TPM11166 A compound extrusion processing aid blend in an LDPE carrier resin commercially produced by Techmer PM recycled resin The film is homopolymer polypropylene (hPP) based metallized with manufacturing waste metallized with approximately 0.02-0.05 pm of physically vapor-deposited aluminum that was crumbled and recycled into extrudable oval granules. ADCA mixed foam of cryogenically crosslinked polypropylene / polyethylene from pulverized manufacturing waste (PP-PE-XE): The particle size distribution of the pulverized foam was measured using a Ro-Tap® sieve shaker with US standard sieves constructed in accordance with ASTM E11. The particle size distribution was measured as: l Lbonn / eznz / B / γΐΛΐ Component Description ADCA 20 US standard sieve: 0.0% 30 US standard sieve: 2.5% 40 US standard sieve: 26.7% 60 US standard sieve: 31.6% 80 US standard sieve: 14.4% 100 US standard sieve: 6.6% Tray: 18.2% l Lbonn / eznz / B / YiAi (All examples in this disclosure were coextruded using feed block collectors) Example 1 - Article A / B where A = foam and B = film Components A (i.e., foam layer components) including resins (50 wt% Infuse™ OBC 9107, 40 wt% 6232, and 10 wt% Adflex™ Q100F), chemical foaming agent (7.5 wt% PPHR ADCA), crosslinking promoter (2.5 wt% PPHR DVB), antioxidants (5.5 wt% PPHR PR023), and processing aid (2.0 wt% PPHR TPM11166) were fed into a first extruder. The first extruder extruded components A at a specific energy of 12.1 kWh / kg and a temperature of 173°C. Components B (i.e., film layer components), which include resins (100 wt% Adflex™ Q100F), antioxidants (2.75% PPHR PR023), and processing aid (2.0% PPHR PPM11166), were fed into a second extruder. As the first extruder extruded components A, the second extruder simultaneously extruded components B at a specific energy of 39.2 kWh / kg and a temperature of 201°C. Components A and B were coextruded using an 80 / 20 feed block collector to produce a non-foamed, non-crosslinked multilayer sheet approximately 1.33 mm thick (the non-foamed A layer is approximately 0.97 mm thick and the non-foamed B layer is approximately 0.36 mm thick). Figure 1C is a backlit, enlarged photograph of a thin slice of the non-foamed multilayer sheet. After coextrusion, the sheet was crosslinked by electron beam irradiation at a rate of 45 kGy with the component B layer (i.e., the film layer) facing the radiation source. The radiation voltage (650 kV) was selected to ensure fairly uniform exposure throughout the sheet's depth. After crosslinking, the sheet was heated on both surfaces to approximately 450°F (232°C) to obtain a multilayer foam structure with an average thickness of 3.98 mm and an average overall density of 0.102 g / cm³. The foam layer was approximately 388 mm thick, and the film layer was approximately 0.10 mm thick. Furthermore, the overall average gel fraction (crosslinking percentage) of the multilayer foam structure was 45.7%. Figure 1A is a backlit, enlarged photograph of the foam from Example 1 that has been thinly sliced. Figure 1B is a frontlit, non-enlarged photograph of the foam from Example 1 that has been thinly sliced. The surface layer is visible in both Figures 1A and 1B. Example 2 - Article A / B where A = foam and B = foam Components A (i.e., the components of the first foam layer) including resins (50 wt% Infuse™ OBC 9107, 40 wt% 6232 and 10 wt% Adflex™ Q100F), chemical foaming agent (7.5% PPHR ADCA), crosslinking promoter (2.5% PPHR DVB), antioxidants (5.5% PPHR PR023) and processing aid (2.0% PPHR TPM11166) in a first extruder. The first extruder extruded components A at a specific energy of 11.5 kW*h / kg and a temperature of 173°C. The B components (i.e., components of the second foam layer) which include resins (40 wt% of 7250FL, 32.5 wt% of 6232, 15 wt% of Adflex™ Q100F, 12.5 wt% of LLP8501.67), chemical foaming agent (7.5% of PPHR ADCA), a crosslinking promoter (2.75% of PPHR DVB), antioxidants (5.0% of PPHR PR023) and a processing aid (2.0% of PPHR TPM11166) in a second extruder.As the first extruder extruded component A, the second extruder simultaneously extruded component B at a specific energy of 15.5 kW*h / kg and a temperature of 168°C. Components A and B were coextruded using an 80 / 20 feed block collector to produce a non-foamed, non-crosslinked multilayer sheet approximately 1.05 mm thick (the non-foamed A layer is approximately 0.80 mm thick and the non-foamed B layer is approximately 0.25 mm thick). Figure 2C is a backlit enlarged photograph of a thin slice of the non-foamed multilayer sheet. After coextrusion, the sheet was crosslinked by electron beam irradiation at a rate of 45 kGy with the component B layer (i.e., the second foam layer) oriented toward the radiation source. Furthermore, the radiation voltage (650 kV) was selected to ensure fairly uniform exposure throughout the entire depth of the sheet. After crosslinking, the sheet was heated on both surfaces to approximately 450°F (232°C) to obtain a multilayer foam structure with an average thickness of 2.24 mm and an average overall density of 0.133 g / cm³. The first foam layer was approximately 1.61 mm thick, and the second foam layer was approximately 0.63 mm thick. Furthermore, the overall average gel fraction (crosslinking percentage) of the multilayer foam structure was 46.7%. Figure 2A is a backlit, enlarged photograph of the finely sliced ​​foam from Example 2. Figure 2B is a frontlit, non-enlarged photograph of the finely sliced ​​foam from Example 2. Example 3 - Article A / B / A where A = foam and B = foam that includes recycled metallized polyolefin material Components A (i.e., the first and third foam layer components), which include resins (40 wt% 7250FL, 32.5 wt% 6232, 15 wt% Adflex™ Q100F, 12.5 wt% LLP8501.67), chemical foaming agent (7.5 wt% PPHR ADCA), crosslinking promoter (2.75 wt% PPHR DVB), antioxidants (5.0 wt% PPHR PR023), and processing aid (2.0 wt% PPHR TPM11166), were fed into a first and third extruder. The first and third extruders extruded components A at a specific energy of 18.3 kW*h / kg and a temperature of 172°C. The B components (i.e., second components of the recycled foam layer) including resins (40 wt% of 7250FL, 32.5 wt% of 6232, 15 wt% of recycled resin, 12.5 wt% of LLP8501.67), chemical foaming agent (7.5% of PPHR ADCA), a crosslinking promoter (2.75% of PPHR DVB), antioxidants (5.0% of PPHR PR023) and a processing aid (2.0% of PPHR TPM11166) were fed into a second extruder.As the first and third extruders extruded component A, the second extruder extruded component B, simultaneously extruding component B at a specific energy of 16.4 kW*h / kg and a temperature of 169°C. Components A and B were coextruded using a 25 / 50 / 25 feed block collector to produce a non-foamed, non-crosslinked multilayer sheet approximately 1.04 mm thick (the non-foamed A layers l Lbonn / eznz / e / Yi are approximately 0.26 and 0.28 mm thick, and the non-foamed B layer is approximately 0.50 mm thick). Figure 3E is a backlit, enlarged photograph of a thin section of the non-foamed multilayer sheet. After coextrusion, the sheet was crosslinked by electron beam irradiation at a rate of 45 kGy. The radiation voltage (650 kV) was selected to ensure fairly uniform exposure throughout the sheet's depth. After crosslinking, the sheet was heated on both surfaces to approximately 450°F (232°C) to obtain a multilayer foam structure with an average thickness of 2.05 mm and an average overall density of 0.208 g / cm³, where the 1- and 3- foam layers are sandwiched between the 2- recycled foam layer. The combined 1- and 3- foam layers are approximately 1.06 mm thick (each approximately 0.53 mm), and the second recycled foam layer is approximately 0.99 mm thick. Furthermore, the overall average gel fraction (crosslinking percentage) of the multilayer foam structure was 43.2%. Figures 3A–3B are enlarged, backlit photographs of the finely sliced ​​foam from Example 3. Figures 3C–3D are unenlarged, frontlit photographs of the finely sliced ​​foam from Example 3. Example 4 - Article A / B / A where A = foam and B = foam including cryogenically pulverized recycled foam material l Lbonn / cznz / e / Yi Components A (i.e., the 1st and 3rd foam layer components), which include resins (40 wt% 7250FL, 32.5 wt% 6232, 15 wt% Adflex™ Q100F, 12.5 wt% LLP8501 .67), chemical foaming agent (7.5 wt% PPHR ADCA), crosslinking promoter (2.75 wt% PPHR DVB), antioxidants (5.0 wt% PPHR PR023), and processing aid (2.0 wt% PPHR TPM11166), were fed into a first and third extruder. The first and third extruders extruded components A at a specific energy of 18.3 kW*h / kg and a temperature of 172°C. The B components (i.e., 2S recycled foam layer components) including resins (40 wt% of 7250FL, 32.5 wt% of 6232, 15 wt% of recycled crosslinked foam, 12.5 wt% of LLP8501.67), chemical foaming agent (7.5% of PPHR ADCA), crosslinking promoter (2.75% of PPHR DVB), antioxidants (5.0% of PPHR PR023) and processing aid (2.0% of PPHR TPM11166) were fed into a second extruder.As the first and third extruders extruded components A, the second extruder simultaneously extruded components B at a specific energy of 17 kW*h / kg and a temperature of 170°C. Components A and B were coextruded using a 25 / 50 / 25 feed block collector to produce a non-foamed, non-crosslinked multilayer sheet approximately 1.11 mm thick (the non-foamed A layers l Lbonn / eznz / e / Yi are approximately 0.26 and 0.25 mm thick, and the non-foamed B layer is approximately 0.60 mm thick). Figure 4C is a backlit, enlarged photograph of a thin section of the non-foamed multilayer sheet. After coextrusion, the sheet was crosslinked by electron beam irradiation at a rate of 45 kGy. The radiation voltage (650 kV) was selected to ensure fairly uniform exposure throughout the sheet's depth. After crosslinking, the sheet was heated on both surfaces to approximately 450°F (232°C) to obtain a multilayer foam structure with an average thickness of 3.60 mm and an average overall density of 0.130 g / cm³, where the first and third foam layers are sandwiched between the second layer of recycled foam. The combined thickness of the first and third foam layers was approximately 1.90 mm (each approximately 0.95 mm), and the second layer of recycled foam was approximately 1.70 mm thick. Furthermore, the overall average gel fraction (crosslinking percentage) of the multilayer foam structure was 37.9%. Figure 4A is a backlit enlarged photograph of the foam from Example 4. Figure 4B is a frontlit, non-enlarged photograph of the foam from Example 4. Note that in Example 4, the recycled cross-linked foam material was charcoal colored, and this is why the intermediate layer is darker. Extrusion foaming compared to extrusion and foaming An extruded polyethylene foam sheet (a commercially available 0.025-0.026 g / cm³ pool lining wall foam from Gladon Company (Oak Creek, W1) (Gladon Blue 3806)) was compared with two 0.025-0.026 g / cm³ polyethylene foam sheets produced by the methods disclosed herein. The first sheet is Toraypef® 40100-AG00, commercially produced by Torae Industries, Inc. (Shiga, JP). The 40100-AG00 was foamed by radiantly heating the cross-linked sheet with hot air. The second sheet is Toraypef® 40064LCE-STD produced by Toray Plastics (America), Inc. The 40064LCE-STD was foamed by radiantly heating the cross-linked sheet with molten salt on one surface and radiant heat on the other. The surface characteristics of these three samples were tested using a Nanovea ST400 3D profilometer.The test specifications and measurement parameters can be found in Tables 2 and 3 below. As shown in Table 4 below, regardless of the heating method, the extruded foamed material (Gladon Blue 38064) is significantly rougher (exhibiting an average surface roughness (Sa) of 83.9 pm and a maximum height (height between the highest peak and the deepest valley (Sz) of 706 pm) than the extruded foam sheets (40100-AG00 and 40064LCE-STD) (which exhibit an average surface roughness (Sa) between 20.7-65.2 pm and a maximum height (Sz) of 237-592 pm). The surface properties of a chemically crosslinked polyolefin foam sheet (0.067 g / cm³) (ProGame™ XC-Cut 7010 l Lbonn / eznz / e / Yi, commercially produced by the Trocellen Group of Companies) were compared with two physically crosslinked polypropylene / polyethylene blend foam sheets (0.067 g / cm³) (Toraypef® 15030AC17-STD and ToraSoft® 15030SR18-STD) produced by the methods described herein. The chemically crosslinked and physically crosslinked foams were foamed in a post-extrusion process. The surface characteristics of these three samples were tested using a Nanovea ST400 3D profilometer. The probe specifications and measurement parameters can be found in Tables 2 and 3 below. As shown in Table 4 below, the chemically crosslinked foam (XC-Cut 7010) exhibited an average surface roughness (Sa) of 89.5 pm and a maximum height (Sz) of 856 pm.Physically crosslinked foams exhibited an average surface roughness (Sa) of 7.63–23.9 pm and a maximum height (Sz) of 81.0–273 pm. Thus, physically crosslinked foams exhibit significantly smoother surfaces compared to chemically crosslinked foam. Table 2 l Lbonn / eznz / e / Yi P1-OP400C P1-OP1200C Z Resolution (nm) 12 25 Z Accuracy (nm) 60 200 Lateral Resolution (pm) 3.5 4.0 l Lbonn / eznz / e / Yi Table 3 4001 00-AG00, 40064 LCE-STD, 15O3OAC17STD, 1 5030SR18-STD 38064, XC-Cut 7010 Test P1-OP400C P1-OP1200C Acquisition speed 800-1850Hz 200-1500Hz Averaged 1 1 Measured surface 10mm x 10mm 10mm x 10mm Stage size 10mm x 15mm 10mm x 15mm Measurement time 00:49:23 01:31:45 Table 4 So i mi > Sz i mi: Labeled side 400100-AG00 20.7 237 Unlabeled side 400100-AG00 29.5 276 Labeled side 40064 LCE-STD 22.8 281 Unlabeled side 40064 LCE 65.2 592 Gladon Blue 38064 83.9 706 Labeled side 15030AC17-STD 22.7 273 Unlabeled side 15030AC17-STD 7.63 81.0 Labeled side 15030SR18-STD 23.9 261 Unlabeled side 15030SR18-STD 12.7 149 CX-Cut 7010 15100 89.5 856 Testing methods The various properties of the previous examples were measured using the following methods: The specific energy of an extruder can be calculated according to the formula: c. ... ______KW (applied)______ . , Specific energy =---------e------í----- where advance rate (-Λ nr' KW (motor rating) * (% of torque from maximum allowed) * RPM (RPM actually running) * KRPM (maximum extruder capacity) * 0.97 (gearbox efficiency) * bonn / eznz / e / Yi In general, the preferred specific energy values ​​would be at least 0.090 kW*h / kg, preferably at least 0.105 kW*h / kg, and more preferably at least 0.120 kW'h / kg, and even more preferably at least 10 kW'h / kg. The density of the multilayer foam structure can be defined and measured using cross-sectional or overall density, instead of a core density, in accordance with JIS K6767. In general, preferred density values ​​would be 20-250 kg / m3, and more preferably 30-125 kg / m3. The average surface roughness and maximum height (height between the highest peak and the deepest valley) of the multilayer foam structure's surface can be defined and measured using a Nanovea 3D non-contact profilometer. The probe specifications and measurement parameters for measuring the average surface roughness and maximum height can be found in Tables 2 and 3. The average surface roughness for the produced foams can be less than approximately 80 µm, less than approximately 70 µm, less than approximately 50 µm, less than approximately 40 µm, less than approximately 30 µm, less than approximately 25 µm, less than approximately 20 µm, less than approximately 15 µm, and less than approximately 10 µm.The maximum height for the surface of the foams produced can be less than approximately 700 pm, less than approximately 600 pm, less than approximately 300 pm, less than approximately 250 pm, less than approximately 200 pm, less than approximately 150 pm and less than 100 pm. Crosslinking can be measured according to the Toray Gel Fractional Method, where tetralin solvent is used to dissolve non-crosslinked components. Essentially, the non-crosslinked material is dissolved in tetralin, and the degree of crosslinking is expressed as the weight percentage of crosslinked material. The apparatus used to determine the percentage of crosslinking of the polymer includes: 100 mesh (0.0045-inch (0.011 mm) wire diameter); type 304 stainless steel bags; numbered wires and clamps; a Miyamoto thermostatic oil bath apparatus; an analytical balance; a fume hood; a gas burner; a high-temperature oven; an antistatic gun; and 3.5-liter wide-mouth stainless steel containers with lids. The reagents and materials used include high-molecular-weight tetralin solvent, acetone, and silicone oil. Specifically, an empty wire mesh bag is weighed, and the weight is recorded.For each sample, approximately 100 milligrams ± approximately 5 milligrams of sample are weighed and transferred to the wire mesh bag. The weight of the wire mesh bag and sample is recorded, typically in the form of foam cuts. Each bag is attached to the corresponding wire and clamps. When the solvent temperature reaches 130°C, the assembly (bag and sample) is immersed in the solvent. The samples are shaken up and down approximately 5 or 6 times to loosen any air bubbles and thoroughly wet the samples. The samples are then attached to a shaker and shaken for three (3) hours to allow the solvent to dissolve the foam. The samples are then cooled in a fume hood. The samples are washed by shaking up and down approximately 7 or 8 times in a primary acetone container. The samples are then washed a second time in a second acetone wash.The washed samples are washed once more in a third container of fresh acetone as before. The samples are then hung in a fume hood to evaporate the acetone for approximately 1 to 5 minutes. The samples are then dried in a drying oven for approximately 1 hour at 120°C. The samples are cooled for a minimum of approximately 15 minutes. The wire mesh bag is weighed on an analytical balance and the weight recorded. The crosslinking is then calculated using the formula 100*(CA) / (BA), where A = weight of empty wire mesh bag; B = weight of wire bag + foam sample before immersion in tetralin; and C = weight of wire bag + dissolved sample after immersion in tetralin. In general, preferred crosslinking degree values ​​can be 1 Lbonn / eznz / e / Yi. 20-75%, and more preferably 30-60%. The melt flow index (MFI) value for a polymer can be defined and measured according to ASTM D1238 at 230°C for polypropylenes and polypropylene-based materials and at 190°C for polyethylenes and polyethylene-based materials using a 2.16 kg piston for 10 minutes. The test time can be reduced for resins with relatively high melt flow. This application describes several numerical ranges in the text and figures. The disclosed numerical ranges inherently support any range or value within the disclosed numerical ranges, even though a precise limitation of scope is not explicitly stated in the specification, because this invention can be practiced throughout the disclosed numerical ranges. The foregoing description is presented to enable a person skilled in the art to manufacture and use the invention, and is provided in the context of a particular application and its requirements. Several modifications to the preferred embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Therefore, this invention is not intended to be limited to the embodiments shown, but rather the broadest scope compatible with the principles and features described herein should be granted. Finally, the full disclosure of the patents and publications referred to in this application is incorporated herein by reference.

Claims

1. A method for forming a multilayer structure comprising: coextruding: a foam layer comprising: polypropylene or polyethylene; and a chemical foaming agent; and a film layer on one side of the foam layer, the film layer comprising polypropylene or polyethylene.

2. The method according to claim 1, wherein the foam layer comprises polypropylene with a melt flow index of 0.1-25 grams for 10 minutes at 230°C.

3. The method according to claim 1, wherein the foam layer comprises polyethylene with a melt flow index of 0.1-25 grams for 10 minutes at 190°C.

4. The method according to claim 1, wherein the foam layer comprises a crosslinking agent.

5. The method according to claim 1, wherein the chemical foaming agent comprises azodicarbonamide.

6. The method according to claim 1, wherein the foam layer comprises polypropylene and polyethylene.

7. A method for forming a multilayer foam structure comprising: coextruding a foam layer comprising polypropylene or polyethylene and a chemical foaming agent; and a film layer on one side of the foam layer, the film layer comprising polypropylene or polyethylene; irradiating the coextruded layers with ionizing radiation; and foaming the irradiated coextruded layers.

8. The method according to claim 7, wherein the ionizing radiation is selected from the group consisting of alpha rays, beta rays, gamma rays, or electron rays.

9. The method according to claim 7, wherein the coextruded structure is irradiated up to 4 times separately.

10. The method according to claim 8, wherein the ionizing radiation is an electron beam with an accelerating voltage of 200-1500 kV.

11. The method according to claim 10, wherein an absorbed electron beam dosage is 10-500 kGy.

12. The method according to claim 7, wherein the ionizing radiation cross-links the extruded structure to a degree of cross-linking of 20-75%.

13. The method according to claim 7, wherein the foaming comprises heating the irradiated structure with molten salt.

14. The method according to claim 7, wherein the multi-layer foam structure has a density of 20-250 kg / m3.

15. The method according to claim 7, wherein the Lbonn / eznz / e / Yi multilayer foam structure has an average closed cell size of 0.05-1.0 mm.

16. The method according to claim 7, wherein the multi-layer foam structure has a thickness of 0.2-50 mm.

17. The method according to claim 7, wherein an average surface roughness for the foam layer is less than 80 pm.

18. The method according to claim 7, wherein the foam layer comprises polypropylene and polyethylene.

19. A method for forming a multilayer structure comprising: coextruding: a first foam layer comprising: polypropylene or polyethylene; and a first chemical foaming agent; and a second foam layer on one side of the first foam layer, the second foam layer comprising: polypropylene or polyethylene; and a second chemical foaming agent.

20. The method according to claim 19, wherein the first and second layers comprise polypropylene with a melt flow index of 0.1-25 grams for 10 minutes at 230°C.

21. The method according to claim 19, wherein the first and second layers comprise polyethylene with a melt flow index of 0.1-25 grams for 10 minutes at 190°C.

22. The method according to claim 19, wherein the first and second layers comprise a crosslinking agent.

23. The method according to claim 19, wherein the first and second chemical foaming agents comprise azodicarbonamide.

24. The method according to claim 19, wherein the first and second layers comprise polypropylene and polyethylene.

25. A method for forming a multilayer foam structure comprising: coextruding: a first foam layer comprising: polypropylene or polyethylene; and a first chemical foaming agent; and a second foam layer on one side of the first foam layer, the second foam layer comprising: polypropylene or polyethylene; and a second chemical foaming agent; irradiating the coextruded layers with ionizing radiation; and foaming the irradiated coextruded layers.

26. The method according to claim 25, wherein the ionizing radiation is selected from the group consisting of alpha rays, beta rays, gamma rays, or electron beams.

27. The method according to claim 25, wherein the coextruded structure is irradiated up to 4 times separately.

28. The method according to claim 26, wherein the ionizing radiation is an electron beam with an accelerating voltage of 200-1500 kV.

29. The method according to claim 28, wherein an Lbonn / eznz / e / Yi absorbed electron beam dosage is 10-500 kGy.

30. The method according to claim 25, wherein the ionizing radiation cross-links the extruded structure to a degree of cross-linking of 20-75%.

31. The method according to claim 25, wherein the foaming comprises heating the irradiated structure with molten salt.

32. The method according to claim 25, wherein the multi-layer foam structure has a density of 20-250 kg / m3.

33. The method according to claim 25, wherein the multilayer foam structure has an average closed cell size of 0.05-1.0 mm.

34. The method according to claim 25, wherein the multi-layer foam structure has a thickness of 0.2-50 mm.

35. The method according to claim 25, wherein an average surface roughness for the first foam layer is less than 80 pm.

36. The method according to claim 25, wherein the first and second layers comprise polypropylene and polyethylene.