Articles Comprising Tubular Aerosol-Forming Substrates

Abstract

An aerosol-generating article for generating an inhalable aerosol upon heating comprises a number of components including an aerosol-forming substrate. The aerosol-forming substrate is in the form of a hollow tubular segment defining a substrate cavity extending between an upstream end of the aerosol-forming substrate and a downstream end of the aerosol-forming substrate. The aerosol-forming substrate comprises a number of thermally conductive particles and aerosol formers. The combination of the tubular shape and the thermally conductive particles allows for a faster time to first puff, improved efficiency of aerosol extraction, and a lighter weight aerosol-generating article.

Description

[Technical field]

[0001] The present disclosure relates to an aerosol-generating article comprising a tubular aerosol-forming substrate. The present disclosure also relates to a method for making an aerosol-forming substrate for such an article, and to an aerosol-generating system. [Background technology]

[0002] Aerosol-generating articles in which an aerosol-generating substrate, such as a tobacco-containing substrate, is heated rather than burned, are known in the art.Typically, in such heated smoking articles, aerosol is generated by transferring heat from a heat source to a physically separated aerosol-generating substrate or material, which may be located in contact with, within, around, or downstream of the heat source.During the use of the aerosol-generating article, volatile compounds are released from the aerosol-generating substrate by heat transfer from the heat source and are entrained in the air drawn through the aerosol-generating article.As the released compounds cool, they condense to form an aerosol.

[0003] Numerous prior art documents disclose aerosol generating devices for consuming aerosol generating articles. Such devices include, for example, electrically heated aerosol generating devices in which the aerosol is generated by heat transfer from one or more electric heater elements of the aerosol generating device to an aerosol generating substrate of the heated aerosol generating article. For example, an electrically heated aerosol generating device has been proposed that includes an internal heater blade adapted to be inserted into the aerosol generating substrate. It is also known to use an aerosol generating article in combination with an external heating system. For example, WO 2020 / 115151 describes the provision of an external heating element that is arranged around the periphery of the aerosol generating article when the aerosol generating article is received in the cavity of the aerosol generating device. Alternatively, WO 2015 / 176898 proposes an inductively heated aerosol generating article that includes an aerosol generating substrate and a susceptor disposed within the aerosol generating substrate. Summary of the Invention [Problem to be solved by the invention]

[0004] In general, it can be difficult to provide efficient heating of the aerosol-generating substrate throughout the rod of substrate. The portion of the substrate closest to the heating element will necessarily be heated most effectively, while incomplete heat transfer through the substrate means that the portion of the substrate furthest from the heating element may not be heated effectively. Thus, aerosol generation from those portions of the substrate that are not effectively heated will not be optimal, and in some cases, the portions of the substrate may never reach a high enough temperature to generate aerosol during use. For example, as described above, when an external heating element is used to heat the rod of the aerosol-generating substrate, the central portion of the rod of the aerosol-generating substrate is not likely to generate as much aerosol as the outer portions of the rod, and in some cases may not generate any aerosol at all. Thus, overall, aerosol generation from the aerosol-generating rod may be inefficient, and portions of the aerosol-generating substrate are potentially wasted.

[0005] In addition, aerosol is generally not immediately generated by the aerosol-generating substrate upon activation of the heating element because there is a preheat period following activation of the heating element during which the aerosol-generating substrate is heated to the temperature required for aerosol generation. Thus, there may be a relatively long duration between activation of the heating element and generation of a sensory acceptable aerosol for inhalation by the user.

[0006] It is therefore desirable to provide an aerosol-generating article having an aerosol-generating substrate adapted to provide more efficient aerosolization of the aerosol-generating substrate and reduce waste of substrate material such as tobacco. It is also desirable to provide such an aerosol-generating article that can achieve a relatively short pre-heat time, so that a sensory acceptable aerosol can be delivered to the user immediately after the start of heating of the aerosol-generating substrate. It would be desirable to provide such an aerosol-generating article that can provide optimized delivery of aerosol from the aerosol-generating substrate. It would be particularly desirable to provide such an aerosol-generating article with a relatively simple design so that it can be manufactured in a cost-effective manner and incorporated into existing product designs. It would further be desirable to provide such an article that can be easily adapted to be heated by various types of heating devices, including induction heating devices and resistance heating devices.

[0007] Known aerosol-forming substrates typically have relatively low thermal conductivity. The low thermal conductivity of the aerosol-forming substrate may result in a relatively large temperature gradient in the aerosol-forming substrate during use. This may mean that the part of the aerosol-forming substrate located farthest from the heater element does not reach high temperature and therefore does not release as much volatile compound as if the aerosol-forming substrate had a higher thermal conductivity. In other words, the low thermal conductivity of the aerosol-forming substrate may undesirably result in the use of the aerosol-forming substrate being less efficient. [Brief description of the drawings]

[0008] [Figure 1] 1 shows a schematic cross-sectional view of a first embodiment of an aerosol-generating article. [Diagram 2] 2 shows a schematic cross-sectional view of a first embodiment of an aerosol generating system including the article of FIG. 1. [Diagram 3] 2 shows a schematic cross-sectional view of a second embodiment of an aerosol generating system including the article of FIG. 1. [Figure 4] 2 shows a schematic cross-sectional view of a third embodiment of an aerosol generating system including the article of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] According to the present disclosure, there is provided an aerosol-generating article for generating an inhalable aerosol upon heating. The heated aerosol-generating article may comprise a number of components, including an aerosol-forming substrate. The aerosol-forming substrate may be in the form of a hollow tubular segment, and preferably defines a substrate recess extending between an upstream end of the aerosol-forming substrate and a downstream end of the aerosol-forming substrate. The aerosol-forming substrate preferably comprises a number of thermally conductive particles and an aerosol former.

[0010] For example, an aerosol-generating article for generating an inhalable aerosol upon heating may be provided, the aerosol-generating article comprising a plurality of components including an aerosol-forming substrate in the form of a hollow tubular segment defining a substrate cavity extending between an upstream end of the aerosol-forming substrate and a downstream end of the aerosol-forming substrate, the aerosol-forming substrate comprising a plurality of thermally conductive particles and an aerosol former.

[0011] The use of a tubular shape for the aerosol-forming substrate can help to avoid thermal gradient effects on the heating of the substrate. With a tubular shape, the substrate does not have a core, and the aerosol-forming material is concentrated in the region of the substrate that is heated either internally or externally. This allows the efficiency of extraction to be significantly increased, which in turn can reduce the total amount of substrate required for the user experience. The reduction in the mass of the substrate reduces the heating inertia and therefore the time required to heat up to a sufficient temperature, thereby reducing the time to first puff. The use of a thermally conductive substrate can significantly increase the benefits obtained by adopting a tubular substrate shape. The increase in the thermal conductivity of the substrate resulting from the presence of thermally conductive particles can further reduce the heating inertia of the substrate, further reducing the time to first puff, and increasing the overall extraction efficiency. By selecting a specific thermally conductive particle, such as graphite or expanded graphite, the weight of the substrate can be further reduced. Reducing the overall mass of the aerosol-forming substrate required for a proper user experience has many advantages, including reducing the overall thermal inertia and reducing the weight of the aerosol-generating article that includes the substrate. Reducing the weight of the article can provide reduced shipping costs and reduced energy associated with shipping, and can provide tax benefits in certain jurisdictions.

[0012] The aerosol-generating articles according to the invention may be used to particular advantage in aerosol-generating systems which utilize gradual or zonal heating. The aerosol-generating articles according to the invention may also be used to particular advantage in aerosol-generating systems which utilize on-demand heating of the smoke.

[0013] The aerosol-forming substrate may comprise 5 to 95% by weight [wt%] of thermally conductive particles, for example 10 to 90% by weight [wt%] of thermally conductive particles, on a dry weight basis. The aerosol-forming substrate may comprise 7 to 60% by weight of aerosol formers, on a dry weight basis. The aerosol-forming substrate may comprise 2 to 20% by weight of fibres, on a dry weight basis. The aerosol-forming substrate may comprise 2 to 10% by weight of a binder, on a dry weight basis. Each of the thermally conductive particles may comprise one or more of graphite, expanded graphite, graphene, carbon nanotubes, charcoal and diamond.

[0014] Accordingly, there is provided an aerosol-forming substrate comprising, on a dry weight basis, 10-90 wt. % thermally conductive particles, 7-60 wt. % aerosol former, 2-20 wt. % fibres and 2-10 wt. % binder, each of the thermally conductive particles comprising one or more of graphite, expanded graphite, graphene, carbon nanotubes, charcoal and diamond.

[0015] The aerosol-generating article may comprise, on a dry weight basis, 5-95% by weight, such as 10-90% by weight, of thermally conductive particles, each of the thermally conductive particles having a thermal conductivity of at least 1 W / (mK). The thermal conductivity may be measured in at least one direction of the particle. The thermal conductivity may be measured at a temperature of 25 degrees Celsius.

[0016] When the term "thermally conductive particles" is used to refer to particles that include carbon, such as particles that include or consist of one or more of graphite, expanded graphite, graphene, carbon nanotubes, charcoal, and diamond, the thermally conductive particles may be referred to as carbon particles or carbon-containing particles.

[0017] Advantageously, the thermally conductive particles can increase the thermal conductivity of the aerosol-forming substrate. Increasing the thermal conductivity of the substrate can provide a more uniform temperature distribution throughout the substrate during use. This can increase the percentage of the aerosol-forming substrate that reaches a temperature high enough to release the volatile compound, and therefore can increase the efficiency of use of the aerosol-forming substrate. Furthermore, increasing the thermal conductivity of the substrate can allow the heater, e.g., a heating blade configured to heat the substrate, to operate at a lower temperature, and therefore require less power. Furthermore, increasing the thermal conductivity of the substrate can allow the heater to heat the substrate to a temperature that releases the volatile compound in a shorter time. Thus, increasing the thermal conductivity can reduce the time required to form an aerosol that can be inhaled by a user.

[0018] Advantageously, one or both of the fibers and binder may increase the tensile strength of the material forming the aerosol-forming substrate, which may allow, for example, existing manufacturing machinery to be used to produce sheets of the aerosol-forming material that can be formed into tubes to form the aerosol-forming substrate.

[0019] The aerosol-forming substrate may have a thermal conductivity of at least 0.05, 0.1, 0.15, 0.2, 0.22, 0.3, 0.4, or 0.5 W / (mK) in at least one direction, or in all directions, at 25 degrees Celsius. The thermal conductivity may be measured when the moisture content of the substrate is 0-20%, or 5-15%, for example about 10%. The thermal conductivity may be measured when the substrate comprises 0-20% or 5-15% by weight, for example about 10% by weight water. The moisture content or water content of the substrate may be measured using a titration method. The moisture content or water content of the substrate may be measured using the Karl Fisher method.

[0020] Optionally, some or all of the thermally conductive particles comprise at least 10, 30, 50, 70, 90, 95, 98, or 99% carbon by weight.

[0021] Optionally, some or all of the thermally conductive particles are graphite particles. Optionally, some or all of the thermally conductive particles are expanded graphite particles. Optionally, some or all of the thermally conductive particles are graphene particles. Optionally, some or all of the thermally conductive particles are carbon nanotubes or carbon nanotube particles. Optionally, some or all of the thermally conductive particles are charcoal particles. Optionally, some or all of the thermally conductive particles are diamond particles, e.g., synthetic diamond particles. Advantageously, such materials may have a relatively high thermal conductivity.

[0022] Expanded graphite is available in concentrations of 2, 1.8, 1.5, 1.2, 1, 0.8, 0.5, 0.2, 0.1, 0.05, and 0.02 grams per cubic centimeter (g / cm 3 The expanded graphite may have a density of less than 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 0.8, 1, 1.2, 1.5, or 1.8 grams per cubic centimeter (g / cm 3 The expanded graphite may have a density of 0.01 to 3, 0.01 to 2, 0.01 to 1.8, 0.01 to 1.5, 0.01 to 1.2, 0.01 to 1, 0.01 to 0.8, 0.01 to 0.5, 0.02 to 3, 0.02 to 2, 0.02 to 1.8, 0.02 to 1.5, 0.02 to 1.2, 0.02 to 1, 0.02 to 0.8, 0.02 to 0.5, 0.01 to 3, 0.05 to 2, 0.05 to 1.8, 0.05 to 1.5, 0.05 to 1.2, 0.05 to 1, 0.05 to 0.8, 0.05 to 0.5 g / cm 3、 0.1~3, 0.1~2, 0.1~1.8, 0.1~1.5, 0.1~1.2, 0.1~1, 0.1~0.8, 0.1~0.5, 0.2~3, 0.2~2, 0.2~1.8, 0.2~1.5, 0.2~1.2, 0.2~1, 0.2~0.8, 0.2~0.5, 0.5~3, 0.5~2, 0.5~1.8, 0.5~1.5, 0.5~1.2, 0.5~1, 0.5~0.8, 0.8~3, 0.8~2, 0.8~1.8, 0.8~1.5, 0.8~1.2, 0.8~1 grams (g / cm 3 )

[0023] Optionally, according to an embodiment, where each of the thermally conductive particles is not necessarily one or more of graphite, expanded graphite, graphene, carbon nanotubes, charcoal, and diamond, some or all of the thermally conductive particles include a metal. Alternatively, or in addition, some or all of the thermally conductive particles include an alloy. Alternatively, or in addition, some or all of the thermally conductive particles include an intermetallic compound. Advantageously, such materials may have relatively high thermal conductivity.

[0024] Optionally, according to an alternative embodiment, where each of the thermally conductive particles is not necessarily one or more of graphite, expanded graphite, graphene, carbon nanotubes, charcoal, and diamond, some or all of the thermally conductive particles include one or more of silicon carbide, silver, copper, gold, aluminum nitride, aluminum, tungsten, and boron nitride. Optionally, some or all of the thermally conductive particles are silicon carbide particles. Optionally, some or all of the thermally conductive particles are silver particles. Optionally, some or all of the thermally conductive particles are copper particles. Optionally, some or all of the thermally conductive particles are gold particles. Optionally, some or all of the thermally conductive particles are aluminum nitride particles. Optionally, some or all of the thermally conductive particles are aluminum particles. Optionally, some or all of the thermally conductive particles are tungsten particles. Optionally, some or all of the thermally conductive particles are boron nitride particles. Advantageously, such materials may have relatively high thermal conductivity.

[0025] The thermally conductive particles may each have a “particle size.” The meaning of the term “particle size” and methods for measuring particle size are explained below.

[0026] Thermally conductive particles may be characterized by a particle size distribution. The particle size distribution may have particle sizes of the numbers D10, D50, and D90. The particle size of the number D10 is defined such that 10% of the particles have a particle size equal to or less than the particle size of the number D10. Similarly, the particle size of the number D50 is defined such that 50% of the particles have a particle size equal to or less than the particle size of the number D50. Thus, the particle size of the number D50 may also be referred to as the median particle size. The particle size of the number D90 is defined such that 90% of the particles have a particle size equal to or less than the particle size of the number D90. Therefore, if there are 1,000 particles in a distribution, and the particles are arranged in order of increasing particle size, it is expected that the particle size of number D10 will be approximately equal to the particle size of the 100th particle, the particle size of number D50 will be approximately equal to the particle size of the 500th particle, and the particle size of number D90 will be approximately equal to the particle size of the 900th particle.

[0027] The particle size distribution may have particle sizes of volume D10, D50, and D90. The particle size of volume D10 is defined such that 10% of the total volume of all particles is occupied by the total volume of particles having a particle size equal to or smaller than the particle size of volume D10. Similarly, the particle size of volume D50 is defined such that 50% of the total volume of all particles is occupied by the total volume of particles having a particle size equal to or smaller than the particle size of volume D50. Also, the particle size of volume D90 is defined such that 90% of the total volume of all particles is occupied by the total volume of particles having a particle size equal to or smaller than the particle size of volume D90.

[0028] Optionally, the thermally conductive particles have a particle size distribution with a particle size number D10, where the particle size number D10 is at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, or 500 microns.

[0029] Optionally, the thermally conductive particles have a particle size distribution with a particle size number D10, where the particle size number D10 is less than or equal to 1,000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns.

[0030] A compromise must be made when determining particle size. Advantageously, larger thermally conductive particles can significantly increase the thermal conductivity of the aerosol-forming substrate compared to smaller thermally conductive particles. However, larger thermally conductive particles can reduce the space available within the substrate for the aerosol-forming material.

[0031] Optionally, the thermally conductive particles have a particle size distribution with a particle size number D50, where the particle size number D50 is at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, or 500 microns.

[0032] Optionally, the thermally conductive particles have a particle size distribution with a particle size number D50, where the particle size number D50 is less than or equal to 1,000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns.

[0033] Optionally, the thermally conductive particles have a particle size distribution with a particle size number D90, where the particle size number D90 is at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, or 500 microns.

[0034] Optionally, the thermally conductive particles have a particle size distribution with a particle size number D90, where the particle size number D90 is less than or equal to 1,000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns.

[0035] Optionally, the thermally conductive particles have a particle size distribution having a particle size number D10 and a particle size number D90, where the particle size number D90 is 50, 40, 30, 20, 10, or 5 times less than the particle size number D10.

[0036] Optionally, the thermally conductive particles have a particle size distribution having a particle size number D10 and a particle size number D90, where the particle size number D90 is at least 1.5, 2, 3, 5, 10, or 20 times the particle size number D10.

[0037] With regard to particle size distribution, a compromise may need to be made. For example, a tighter particle size distribution, characterized by a smaller ratio between the particle size of D90 and the particle size of D10, may advantageously provide a more uniform thermal conductivity throughout the aerosol-forming substrate. This is because there is less variation in particle size at different locations within the substrate. This may advantageously allow for more efficient use of the aerosol-forming material throughout the aerosol-forming substrate. However, a tighter particle size distribution may disadvantageously be more difficult and expensive to achieve. The inventors have found that the particle size distribution described above may provide an optimal compromise between these two factors.

[0038] Optionally, the thermally conductive particles have a particle size distribution with a particle size in volume D10, where the particle size in volume D10 is at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, or 500 microns.

[0039] Optionally, the thermally conductive particles have a particle size distribution with a particle size in volume D10, wherein the particle size in volume D10 is less than or equal to 1,000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns.

[0040] Optionally, the thermally conductive particles have a particle size distribution with a particle size by volume D50, where the particle size by volume D50 is at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, or 500 microns.

[0041] Optionally, the thermally conductive particles have a particle size distribution with a particle size by volume D50 of less than or equal to 1,000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns.

[0042] Optionally, the thermally conductive particles have a particle size distribution with a particle size by volume D90, where the particle size by volume D90 is at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, or 500 microns.

[0043] Optionally, the thermally conductive particles have a particle size distribution with a particle size by volume D90 of less than or equal to 1,000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns.

[0044] It may be particularly preferred that the thermally conductive particles have a particle size distribution with a particle size volume D10 of 1 to 20 microns. Alternatively or additionally, it may be particularly preferred that the thermally conductive particles have a particle size distribution with a particle size volume D90 of 50 to 300 microns, or 50 to 200 microns.

[0045] Optionally, the thermally conductive particles have a particle size distribution having a particle size in volume D10 and a particle size in volume D90, where the particle size in volume D90 is no greater than 50, 40, 30, 20, 10, or 5 times the particle size in volume D10.

[0046] Optionally, the thermally conductive particles have a particle size distribution having a particle size in volume D10 and a particle size in volume D90, where the particle size in volume D90 is at least 1.5, 2, 3, 5, 10, or 20 times the particle size in volume D10.

[0047] As explained above, a compromise has to be made with respect to particle size distribution and the inventors have found that the above particle size distribution may provide an optimal compromise.

[0048] Optionally, each of the thermally conductive particles has a particle size of at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, or 500 microns. Optionally, each of the thermally conductive particles has a particle size of 1,000, 500, 300, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns or less. It may be particularly preferred that each of the thermally conductive particles has a particle size of at least 1 micron. Alternatively or additionally, it may be particularly preferred that each of the thermally conductive particles has a particle size of 300 microns or less. Particles less than 1 micron may be difficult to handle during manufacturing. In addition, particles less than 1 micron may be more likely to pass through a filter in an aerosol-generating article with an aerosol-forming substrate. Particles greater than 300 microns may occupy a significant amount of space within a substrate that may be used for the aerosol-forming material. Therefore, it may be particularly advantageous for each of the thermally conductive particles to have a particle size of at least 1 micron, or a particle size of no more than 300 microns, or both.

[0049] Optionally, each of the thermally conductive particles has three mutually orthogonal dimensions, the largest of the three dimensions being no greater than 10, 8, 5, 3, or 2 times the smallest of the three dimensions. Optionally, each of the thermally conductive particles has three mutually orthogonal dimensions, the largest of the three dimensions being no greater than 10, 8, 5, 3, or 2 times the second largest of the three dimensions. Optionally, each of the thermally conductive particles is substantially spherical. Advantageously, the orientation of substantially spherical particles may not affect the thermal conductivity of the substrate as much as the orientation of non-spherical particles. Thus, the use of more spherical particles may result in reduced variation between different substrates where the orientation of the particles is not controlled. Additionally, substantially spherical particles may be easier to characterize.

[0050] Optionally, the thermally conductive particles comprise at least 10, 20, 50, 100, 200, 500, or 1000 particles. Advantageously, a greater number of particles in the aerosol-forming substrate may allow for a more uniform thermal conductivity of the substrate.

[0051] Optionally, the substrate comprises at least 20, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, or 85% by weight of thermally conductive particles on a dry weight basis. Optionally, the substrate comprises no more than 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, or 15% by weight of thermally conductive particles on a dry weight basis. Optionally, the substrate comprises 10-90, 20-90, 30-90, 40-90, 50-90, 60-90, 70-90, 80-90, 10-80, 20-80, 30-80, 40-80, 50-80, 60-80, 70-80, 10-70, 20-70, 30-70, 40-70, 50-70, 60-70, 10-60, 20-60, 30-60, 40-60, 50-60, 10-50, 20-50, 30-50, 40-50, 10-40, 20-40, 30-40, 10-30, 20-30, or 10-20 weight percent thermally conductive particles on a dry weight basis. It may be particularly preferred for the substrate to comprise from 50 to 90, or more preferably from 60 to 90, or even more preferably from 65 to 85, weight percent of thermally conductive particles on a dry weight basis.

[0052] A compromise may need to be made with respect to the weight percent of thermally conductive particles in the substrate. Increasing the weight percent of particles in the aerosol-forming substrate may advantageously increase the thermal conductivity of the substrate. However, increasing the weight percent of particles in the aerosol-forming substrate may also reduce the space available to one or more of the aerosol formers, binders, and fibers, which may result in a substrate that forms less aerosol or has less tensile strength.

[0053] Optionally, the substrate comprises at least 10, 15, 20, 25, 30, 35, 40, 45, 50, or 55% by weight of the aerosol former on a dry weight basis. Optionally, the substrate comprises no more than 55, 50, 45, 40, 35, 30, 25, 20, or 15% by weight of the aerosol former on a dry weight basis. Optionally, the substrate comprises 7-60, 10-60, 20-60, 30-60, 40-60, 50-60, 7-50, 10-50, 20-50, 30-50, 40-50, 7-40, 10-40, 20-40, 30-40, 7-30, 10-30, 20-30, 7-20, 10-20, or 7-10% by weight of the aerosol former on a dry weight basis. It may be particularly preferred for the substrate to contain from 15 to 25 weight percent aerosol former on a dry weight basis.

[0054] Optionally, the aerosol former comprises or consists of one or more of polyhydric alcohols (such as propylene glycol, polyethylene glycol, triethylene glycol, 1,3-butanediol, and glycerin), esters of polyhydric alcohols (such as glycerol monotriacetate, glycerol diacetate, or glycerol triacetate), and aliphatic esters of mono-, di-, or polycarboxylic acids (such as dimethyl dodecanedioate and dimethyl tetradecanedioate). Optionally, the aerosol-forming substrate comprises one or both of glycerin and glycerol.

[0055] Optionally, the substrate comprises at least 2, 4, 6, 8, 10, 12, 14, 16, or 18% by weight of fibers on a dry weight basis. Optionally, the substrate comprises no more than 20, 18, 16, 14, 12, 10, 8, 6, or 4% by weight of fibers on a dry weight basis. Optionally, the substrate comprises no more than 4-20, 6-20, 8-20, 10-20, 12-20, 14-20, 16-20, 18-20, 2-18, 4-18, 6-18, 8-18, 10-18, 12-18, 14-18, 16-18, 2-16, 4-16, 6-16, 8-16, 10 % fibers by weight. It may be particularly preferred for the substrate to comprise 2 to 10% by weight fibers by weight on a dry weight basis.

[0056] Optionally, the fibers are cellulose fibers. Advantageously, cellulose fibers are not overly expensive and can increase the tensile strength of the substrate.

[0057] Optionally, each of the fibers has three mutually orthogonal dimensions, the largest of the three dimensions being at least 1.5, 2, 3, 5, 10, or 20 times greater than the smallest of the three dimensions. Optionally, each of the fibers has three mutually orthogonal dimensions, the largest of the three dimensions being at least 1.5, 2, 3, 5, 10, or 20 times greater than a second largest of the three dimensions.

[0058] Optionally, the substrate comprises at least 4, 6, or 8% by weight of binder on a dry weight basis. Optionally, the substrate comprises no more than 8, 6, or 4% by weight of binder on a dry weight basis. Optionally, the substrate comprises 4-10, 6-10, 8-10, 2-8, 4-8, 6-8, 2-6, 4-6, 2-4% by weight of binder on a dry weight basis. It may be particularly preferred for the substrate to comprise 2-10% by weight of binder on a dry weight basis.

[0059] Suitable binders are known in the art and include, but are not limited to, natural pectins (such as fruit pectins, citrus pectins, or tobacco pectins), guar gums (such as hydroxyethyl guar, hydroxypropyl guar), locust bean gums (such as hydroxyethyl locust bean gum, hydroxypropyl locust bean gum), alginates, starches (such as modified or derivatized starches), celluloses (such as methylcellulose, ethylcellulose, ethylhydroxymethylcellulose, carboxymethylcellulose), tamarind gum, dextran, pralon, konjac flour, xanthan gum, and the like. It may be particularly preferred that the binder is or comprises guar. It may be particularly preferred that the binder comprises or consists of one or more of carboxymethylcellulose or hydroxypropylcellulose, or gums such as guar gum.

[0060] Optionally, the thermally conductive particles are substantially homogeneously distributed throughout the aerosol-forming substrate. Optionally, the aerosol formers are substantially homogeneously distributed throughout the aerosol-forming substrate. Optionally, the fibers are substantially homogeneously distributed throughout the aerosol-forming substrate. Optionally, the binder is substantially homogeneously distributed throughout the aerosol-forming substrate. Advantageously, homogeneous distribution of the substrate's components may result in the substrate having more spatially uniform properties. For example, substantially homogeneously distributed thermally conductive particles may result in the substrate having a substantially uniform thermal conductivity. As another example, substantially homogeneously distributed binder or fibers may result in the substrate having a substantially uniform tensile strength.

[0061] Optionally, the substrate comprises nicotine. Optionally, the substrate comprises at least 0.01, 1, 2, 3, or 4% by weight of nicotine on a dry weight basis. Optionally, the substrate comprises no more than 5, 4, 3, 2, or 1% by weight of nicotine on a dry weight basis. Optionally, the substrate comprises 0.01-5, 1-5, 2-5, 3-5, 4-5, 0.01-4, 1-4, 2-4, 3-4, 0.01-3, 1-3, 2-3, 0.01-2, 1-2, 0.01-1% by weight of nicotine on a dry weight basis. It may be particularly preferred for the substrate to comprise 0.5-4% by weight of nicotine on a dry weight basis.

[0062] Optionally, the nicotine is substantially homogeneously distributed throughout the aerosol-forming substrate.

[0063] Optionally, the substrate comprises an acid. Optionally, the substrate comprises at least 0.01, 1, 2, 3, or 4 weight percent acid on a dry weight basis. Optionally, the substrate comprises no more than 5, 4, 3, 2, or 1 weight percent acid on a dry weight basis. Optionally, the substrate comprises 0.01-5, 1-5, 2-5, 3-5, 4-5, 0.01-4, 1-4, 2-4, 3-4, 0.01-3, 1-3, 2-3, 0.01-2, 1-2, 0.01-1 weight percent acid on a dry weight basis. It may be particularly preferred for the substrate to comprise 0.5-5 weight percent acid on a dry weight basis.

[0064] Optionally, the acid comprises or consists of one or more of fumaric acid, lactic acid, benzoic acid, and levulinic acid.

[0065] Optionally, the acid is distributed substantially homogeneously throughout the aerosol-forming substrate.

[0066] Optionally, the substrate comprises at least one plant. Optionally, the substrate comprises at least 0.01, 1, 2, 5, 10, or 15% by weight, on a dry weight basis, of at least one plant. Optionally, the substrate comprises no more than 20, 15, 10, 5, 2, or 1% by weight, on a dry weight basis, of at least one plant. Optionally, the substrate comprises 0.01-20, 1-20, 2-20, 5-20, 10-20, 15-20, 0.01-15, 1-15, 2-15, 5-15, 10-15, 0.01-10, 1-10, 2-10, 5-10, 0.01-5, 1-5, 2-5, 0.01-2, 1-2, 0.01-1% by weight, on a dry weight basis, of at least one plant. It may be particularly preferred for the substrate to comprise from 1 to 15% by weight, on a dry weight basis, of at least one plant.

[0067] Optionally, the at least one plant comprises or consists of one or both of clove and rosmarinus.

[0068] Optionally, the at least one plant is substantially homogeneously distributed throughout the aerosol-forming substrate.

[0069] Optionally, the substrate comprises at least one flavourant. Optionally, the substrate comprises at least 0.1, 1, 2, or 5% by weight, on a dry weight basis, of at least one flavourant. Optionally, the substrate comprises no more than 10, 5, 2, or 1% by weight, on a dry weight basis, of at least one flavourant. Optionally, the substrate comprises 0.1-10, 1-10, 2-10, 5-10, 0.1-5, 1-5, 2-5, 0.1-2, 1-2, 0.1-1% by weight, on a dry weight basis, of at least one flavourant. It may be particularly preferred for the substrate to comprise 0.1-5% by weight, on a dry weight basis, of at least one flavourant.

[0070] Optionally, the at least one flavourant is present as a coating, for example a coating on one or more other components of the aerosol-forming substrate. Alternatively, or in addition, the at least one flavourant is substantially homogeneously distributed throughout the aerosol-forming substrate.

[0071] Optionally, the aerosol-forming substrate comprises at least one organic material, such as tobacco. Optionally, the at least one organic material comprises one or more of herb leaves, tobacco leaves, tobacco stem fragments, reconstituted tobacco, homogenized tobacco, extruded tobacco, and expanded tobacco. Optionally, the at least one organic material is distributed substantially homogeneously throughout the aerosol-forming substrate.

[0072] The substrate may contain less than 10, 5, 3, 2 or 1% by weight of tobacco on a dry weight basis.Optionally, the aerosol-forming substrate is a tobacco-free aerosol-forming substrate.

[0073] The tubular segment of the aerosol-forming substrate may be described as a rod. Thus, a rod of aerosol-forming substrate may be provided.

[0074] The aerosol-forming substrate is preferably in the form of a tube having an outer diameter, an inner diameter and a length, the length of the tube being 5 mm to 100 mm, the outer diameter being 3 mm to 20 mm, and the inner diameter being 2.5 mm to 19.5 mm. The length of the tube may be 8 mm to 25 mm, the outer diameter of the tube may be 6 mm to 8 mm, and the inner diameter of the tube may be 5 mm to 7.9 mm.

[0075] The susceptor elements may be located within the rod of the aerosol-forming substrate. The susceptor elements may be elongated susceptor elements. The susceptor elements may extend longitudinally within the rod of the aerosol-forming substrate, for example in contact with the inner surface of the tubular aerosol-generating substrate. The rod may be substantially cylindrical, for example a right cylinder. The susceptor elements may extend all the way to the downstream end of the rod of the aerosol-forming substrate. The susceptor elements may extend all the way to the upstream end of the rod of the aerosol-forming substrate. The susceptor elements may have substantially the same length as the rod of the aerosol-forming substrate. The susceptor elements may extend from the upstream end to the downstream end of the rod of the aerosol-forming substrate. The susceptor elements may be in the form of pins, rods, strips or blades. The susceptor elements may have a length of 5 to 15 millimeters, 6 to 12 millimeters, or 8 to 10 millimeters. The susceptor elements may have a width of 1 to 5 millimeters. The susceptor element may have a thickness of 0.01 to 2 millimeters, 0.5 to 2 millimeters, or 0.5 to 1 millimeter.

[0076] Alternatively, there may be no susceptor material within the aerosol-forming substrate or within the rod of the aerosol-forming substrate.

[0077] Optionally, some or each of the thermally conductive particles may be inductively heatable, for example to a temperature of at least 100 degrees Celsius, 150 degrees Celsius, or 200 degrees Celsius. Optionally, some or each of the thermally conductive particles may comprise or consist of one or more susceptor materials. Advantageously, this may allow the thermally conductive particles to be inductively heatable. The thermally conductive particles may comprise or be the only susceptor material present within the aerosol-forming substrate or within the rod of the aerosol-forming substrate. That is, there may be cases where there are no susceptor elements present within the aerosol-forming substrate or within the rod of the aerosol-forming substrate, except for the thermally conductive particles or the carbon particles.

[0078] Suitable susceptor materials include, but are not limited to, carbon, carbon-based materials, graphene, graphite, expanded graphite, molybdenum, silicon carbide, stainless steel, niobium, aluminum, nickel, nickel-containing compounds, titanium, and composites of metal materials. Suitable susceptor materials may include ferromagnetic materials, such as ferritic iron, ferromagnetic steel or stainless steel, ferromagnetic particles, and ferrites. Suitable susceptor materials may be or include aluminum. The susceptor material preferably includes more than 5% ferromagnetic or paramagnetic materials, preferably more than 20% ferromagnetic or paramagnetic materials, and more preferably more than 50% or more than 90% ferromagnetic or paramagnetic materials. Preferred susceptor materials may include metals, metal alloys, or carbon.

[0079] Particularly preferred susceptor materials may be or include carbon, carbon-based materials, graphene, graphite, or expanded graphite. Advantageously, such materials have relatively high thermal conductivity, relatively low density, and may be inductively heated.

[0080] Optionally, the aerosol-forming substrate has a thermal conductivity in at least one direction at 25 degrees Celsius of greater than 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.75, 1, 1.25, 1.5, 2, 5, 10, 20, 50, 100, 200, or 500 W / (mK).

[0081] Optionally, the aerosol-forming substrate has a viscosity of 1500, 1450, 1400, 1350, 1300, 1250, 1200, 1100, 1050, 1000, 950, 900, 850, 800, 850, 800, 750, 700, 650, or 600 kg / m 3 Optionally, the aerosol-forming substrate has a density of from 600 to 1400 kg / m 3 , 800~1200kg / m 3 , or 900-1100kg / m 3 Advantageously, by reducing the density of the substrate, the cost of shipping the substrate may be reduced.

[0082] Optionally, the aerosol-forming substrate has a moisture content of 1-20, or 3-15% by weight. The moisture content may be measured after equilibration at 20 degrees Celsius and 50% relative humidity for 48 hours. Optionally, the aerosol-forming substrate comprises 1-20, or 3-15% water by weight. The moisture content or moisture content of the substrate may be measured using a titration method. The moisture content or moisture content of the substrate may be measured using the Karl Fisher method.

[0083] Optionally, the aerosol-forming substrate is formed from a sheet of aerosol-forming material that is rolled to form a tubular segment. Thus, the hollow tubular segment may be a rolled sheet of aerosol-forming material, e.g., a rolled sheet of homogenized tobacco material, or, e.g., a rolled sheet of tobacco-free aerosol-forming material.

[0084] The aerosol-forming substrate may have a thickness equivalent to a sheet of a single layer of aerosol-forming material. The aerosol-forming substrate may have a thickness equivalent to a sheet of two or more layers. The sheet of aerosol-forming material may have a thickness of at least 5, 10, 20, 50, 100, 150, or 200 microns. Optionally, the sheet or strip may have a thickness of no more than 2000, 1000, 500, 400, 300, or 250 microns. Optionally, the sheet may have a thickness of 100 to 350 microns, or 150 to 300 microns.

[0085] Optionally, the sheet of aerosol-forming material has a mass of at least 20, 50, or 100 g / m 2 Optionally, the sheet or strip has a basis weight of 300 g / m 2 Optionally, the sheet has a basis weight of 20 to 300 g / m 2 , 50~250g / m 2 , or 100~250g / m 2 The sheet has a basis weight of 1.0 g.

[0086] Optionally, the sheet has a viscosity of at least 0.1, 0.2, 0.3, or 0.5 g / m 3 Optionally, the sheet has a density of 2, 1.5, 1.2, or 1 g / m 3 Optionally, the sheet has a density of 0.1 to 2 g / m 3 , 0.2~2g / m 3 , 0.3~2g / m 3 , 0.3~1.5g / m 3 , or 0.3 to 1.2 g / m 3 has a density of

[0087] The hollow tubular segment may be an extruded tube of aerosol-forming material, for example an extruded tube of homogenized tobacco material, or for example an extruded tube of aerosol-forming material that does not include tobacco.

[0088] The aerosol-generating article may be in the form of a rod and may comprise multiple components, including an aerosol-forming substrate assembled within a wrapper or housing.

[0089] Optionally, the aerosol-generating article comprises a front plug. Optionally, the aerosol-generating article comprises a first hollow tube, e.g., a first hollow acetate tube. Optionally, the aerosol-generating article comprises a second hollow tube, e.g., a second hollow acetate tube. Optionally, the second hollow tube comprises one or more vent holes. Optionally, the aerosol-generating article comprises a mouth-side plug filter. Optionally, the aerosol-generating article comprises a wrapper, e.g., a paper wrapper.

[0090] Optionally, the front plug is disposed at the most upstream end of the article. Optionally, the aerosol-forming substrate is disposed downstream of the front plug. Optionally, the first hollow tube is disposed downstream of the aerosol-forming substrate. Optionally, the second hollow tube is disposed downstream of the first hollow tube. Optionally, the mouth plug filter is disposed downstream of one or both of the first hollow tube and the second hollow tube. Optionally, the mouth plug filter is disposed at the most downstream end of the article. Optionally, the most downstream end of the article, which may also be referred to as the mouth end of the article, may be configured to be inserted into the mouth of a user. The user may, for example, be able to directly inhale the mouth end of the article.

[0091] Optionally, the front plug, the tubular aerosol-forming substrate, one or both of the first and second hollow tubes, and the oral plug filter are surrounded by a wrapper, for example a paper wrapper.

[0092] Optionally, the front plug has a length of 2-10 mm, 3-8 mm, or 4-6 mm, for example, about 5 mm. Optionally, the aerosol-forming substrate has a length of 5-20 mm, 8-15 mm, or 10-15 mm, for example, about 12 mm. Optionally, the first hollow tube has a length of 2-20 mm, 5-15 mm, or 5-10 mm, for example, about 8 mm. Optionally, the second hollow tube has a length of 2-20 mm, 5-15 mm, or 5-10 mm, for example, about 8 mm. Optionally, the oral plug filter has a length of 5-20 mm, 8-15 mm, or 10-15 mm, for example, about 12 mm. The length of one or more of the front plug, the aerosol-forming substrate, the first hollow tube, the second hollow tube, and the oral plug filter may extend longitudinally.

[0093] One or more of the front plug, the aerosol-forming substrate, the first hollow tube, the second hollow tube, and the oral plug filter may be substantially cylindrical in shape, for example a right cylinder.

[0094] According to one aspect of the present disclosure, an aerosol generation system is provided.

[0095] The system may comprise an aerosol generating article and an electrical aerosol generating device. The article may be as described above, for example the article according to the third aspect.

[0096] Optionally, the electrical aerosol generating device is configured, in use, to resistively heat the aerosol-generating article.

[0097] Optionally, the electrical aerosol generating device is configured, in use, to inductively heat the aerosol-generating article, for example an aerosol-forming substrate of the aerosol-generating article.

[0098] According to the present disclosure, there is provided a method of forming a hollow tubular aerosol-forming substrate, such as a substrate for an aerosol-generating article as described above. The method may include forming a slurry including one or more or all of thermally conductive particles, aerosol formers, fibers, and a binder. The method may include casting and drying the slurry to form the aerosol-forming substrate, or extruding the slurry to form the aerosol-forming substrate, or casting and drying the slurry to form a precursor, such as a sheet of the aerosol-forming substrate, and then forming the precursor into the aerosol-forming substrate.

[0099] Optionally, the slurry comprises water. Optionally, the slurry comprises 20-90, 30-90, 40-90, 40-85, 50-80, 60-80, or 60-7 wt % water.

[0100] Optionally, the slurry comprises an acid. Optionally, the acid comprises or consists of one or more of fumaric acid, lactic acid, benzoic acid, and levulinic acid.

[0101] Optionally, the slurry comprises nicotine.

[0102] Optionally, forming the slurry includes forming a first mixture. The first mixture may include an aerosol former. The first mixture may include fibers. The first mixture may include water. The first mixture may include an acid. The first mixture may include nicotine. Forming the slurry may include forming a second mixture. The second mixture may include thermally conductive particles. The second mixture may include a binder. Forming the slurry may include adding the second mixture to the first mixture to form a combined mixture.

[0103] Thus, forming a slurry includes: forming a first mixture including an aerosol former, fibers, water, optionally an acid, and optionally nicotine; forming a second mixture comprising thermally conductive particles and a binder; and adding the second mixture to the first mixture to form a combined mixture.

[0104] The combined mixture can then be formed into a slurry, for example, by mixing.

[0105] Optionally, forming the first mixture includes providing an aerosol former, or a solution including an aerosol former and nicotine.

[0106] Optionally, forming the first mixture includes adding an acid to the aerosol former, or to a solution including the aerosol former and nicotine, to form a first pre-mixture.

[0107] Optionally, forming the first mixture includes adding water to the aerosol former, or to a solution including the aerosol former and nicotine, or to the first pre-mixture to form a second pre-mixture.

[0108] Optionally, forming the first mixture includes adding fibers to the second pre-mixture.

[0109] Optionally, forming the second mixture includes mixing the thermally conductive particles with a binder.

[0110] Optionally, the method, e.g., forming a slurry, includes a first mixing of the combined mixture. Optionally, the first mixing is performed under a first pressure of less than or equal to 500, 400, 300, 250, or 200 mbar. Optionally, the first mixing is performed for 1-10 minutes, 2-8 minutes, or 3-6 minutes, e.g., about 4 minutes.

[0111] Optionally, the method, e.g., forming a slurry, includes a second mixing after the first mixing. Optionally, the second mixing is performed under a second pressure less than the first pressure. Optionally, the second pressure is less than or equal to 500, 400, 300, 200, 150, or 100 mbar. Optionally, the second mixing is performed for 5-120 seconds, 5-80 seconds, 5-40 seconds, or 10-30 seconds, e.g., about 20 seconds.

[0112] Optionally, casting the slurry includes casting the slurry onto a flat support, for example a steel flat support.

[0113] Optionally, after casting the slurry and before drying the slurry, the method includes setting a thickness of the slurry, for example, setting a thickness of the slurry to between 100 and 1200 microns, between 200 and 1000 microns, between 300 and 900 microns, between 500 and 700 microns, for example, about 600 microns.

[0114] Optionally, drying the slurry includes providing a stream of gas, such as air, over or through the slurry. Optionally, the stream of gas is heated. Optionally, the stream of gas is heated to a temperature of 100-160 degrees Celsius, or 120-140 degrees Celsius. Optionally, the stream of gas is provided for 1-10 minutes, or 2-5 minutes. Optionally, drying the slurry includes drying the slurry until the slurry has a moisture content of 1-20, 2-15, 2-10, or 3-7% by weight.

[0115] Optionally, the slurry is dried to form a precursor for forming into an aerosol-forming substrate, the precursor being a sheet of aerosol-forming material. Optionally, the method includes cutting the sheet of aerosol-forming material.

[0116] The sheet of aerosol-forming material may be formed into an aerosol-forming substrate by rolling a sheet of the aerosol-forming substrate into a tube. Thus, the walls of the tube are formed from the sheet of aerosol-forming material. The tubular shape may be maintained by overlapping a portion of the rolled sheet and attaching the overlapped portion with an adhesive such as gum. The walls of the tube formed by rolling the sheet of aerosol-forming material may have a thickness equal to the thickness of the sheet of aerosol-forming material, i.e., the tube may be formed from a single layer of the sheet of aerosol-forming material. However, the walls of the tube may be formed from multiple layers of the sheet rolled into the form of a tube. Once rolled and secured, the tube of aerosol-forming material may be cut to length to form a tubular segment of the aerosol-forming substrate.

[0117] As will be understood by one of ordinary skill in the art upon reading this disclosure, features described herein in relation to one embodiment may be applicable to any other embodiment.

[0118] The term "aerosol-forming substrate" as used herein may refer to a substrate capable of emitting an aerosol or volatile compound capable of forming an aerosol. Such a volatile compound may be emitted by heating the aerosol-forming substrate. The aerosol-forming substrate may comprise an aerosol-forming material. The aerosol-forming substrate may be adsorbed, coated, impregnated, or otherwise loaded onto a carrier or support. The aerosol-forming substrate may conveniently be part of an aerosol-generating article or a smoking article.

[0119] As used herein, the term "thermally conductive particles" may refer to particles having a thermal conductivity of greater than 0.3, preferably 0.5, or more preferably 1 W / (mK) in at least one direction at 25 degrees Celsius, for example, in all directions at 25 degrees Celsius. The particles may exhibit anisotropic or isotropic thermal conductivity.

[0120] As used herein, the term "expanded graphite" may refer to a graphite-based material or a material having a graphite-like structure. The expanded graphite may have carbon layers (e.g., similar to graphite) where the spacing between the carbon layers is greater than the spacing found between the carbon layers of regular graphite. The expanded graphite may have carbon layers with elements or compounds interposed within the spaces between the carbon layers.

[0121] The term "particle size" as used herein may refer to a single dimension and may be used to characterize a given particle size. The dimension may be the diameter of a spherical particle that occupies the same volume as the given particle. All particle sizes and particle size distributions herein may be obtained using standard laser diffraction techniques. The particle sizes and particle size distributions described herein may be obtained using commercially available sensors, such as Sympatec's HELOS laser diffraction sensor.

[0122] The term "density" as used herein may be used to refer to true density unless otherwise specified. Thus, unless otherwise specified, the density of a powder or particles may refer to the true density of the powder or particles (rather than the bulk density of the powder or particles, which may vary significantly depending on how the powder or particles are handled). Measurement of true density can be performed using many standard methods, which are often based on Archimedes' principle. When used to measure the true density of a powder, the most widely used method involves the powder being placed and weighed inside a container of known volume (pycnometer). The pycnometer is then filled with a fluid of known density in which the powder is not soluble. The volume of the powder is determined by the difference between the volume indicated by the pycnometer and the volume of the added liquid (i.e., the volume of air displaced).

[0123] As used herein, the term "aerosol-generating article" may refer to an article that is capable of generating or releasing an aerosol, for example, when heated.

[0124] As used herein, the term "longitudinal direction" may refer to the direction extending between a downstream or proximal end and an upstream or distal end of a component, such as an aerosol-forming substrate or an aerosol-generating article.

[0125] As used above, the term "transverse" may refer to a direction perpendicular to the longitudinal axis.

[0126] As used herein, the term "aerosol generating device" may refer to a device for use with an aerosol-generating article to enable the generation or emission of an aerosol.

[0127] As used herein, the term "sheet" can refer to a generally planar, laminar element having a width and length that is substantially greater than its thickness, for example, at least 2, 3, 5, 10, 20, or 50 times.

[0128] The term "aerosol former" as used herein may refer to any suitable known compound or mixture of compounds that, upon use, facilitates the formation of an aerosol. The aerosol may be a dense and stable aerosol. The aerosol may be substantially resistant to thermal decomposition at the operating temperature of the aerosol-forming substrate or aerosol-generating article.

[0129] The term "aerosol cooling element" as used herein may refer to a component of an aerosol-generating article that is located downstream of an aerosol-forming substrate such that, in use, an aerosol formed by the substrate or by volatile compounds released from the aerosol-forming substrate passes through and is cooled by the aerosol cooling element before being inhaled by a user.

[0130] As used herein, the term "rod" may refer to a generally cylindrical element, for example a right cylindrical element of substantially circular, oval, or elliptical cross section.

[0131] The term "ventilation level" as used herein may refer to the volume ratio of the airflow entering the aerosol-generating article through the ventilation zone (ventilation airflow) to the sum of the aerosol airflow and the ventilation airflow. The higher the ventilation level, the higher the dilution of the aerosol stream delivered to the consumer.

[0132] [Example] The present invention is defined in the claims. However, below is provided a non-exhaustive list of non-limiting examples, any one or more of the features of these examples may be combined with any one or more of the features of other examples, embodiments, or aspects described herein.

[0133] Example i. An aerosol-generating article for producing an inhalable aerosol comprising a hollow tubular aerosol-forming substrate, the aerosol-forming substrate comprising a plurality of thermally conductive particles and an aerosol former. Example 1. 1. An aerosol-generating article for generating an inhalable aerosol upon heating, the aerosol-generating article comprising a plurality of components including an aerosol-forming substrate, the aerosol-forming substrate being in the form of a hollow tubular segment defining a substrate cavity extending between an upstream end of the aerosol-forming substrate and a downstream end of the aerosol-forming substrate, the aerosol-forming substrate comprising a plurality of thermally conductive particles and an aerosol former. Example 2. The aerosol-generating article of example i or 1, wherein each of the plurality of thermally conductive particles has a thermal conductivity of greater than 1, 2, 5, 10, 20, 50, 100, 200, 500, or 1000 W / mK. Example 3. An aerosol-generating article according to any of Examples 1 and 2, wherein the aerosol-forming substrate comprises, on a dry weight basis, 5 to 95% by weight, for example 10 to 90% by weight, of thermally conductive particles, each of the thermally conductive particles having a thermal conductivity of at least 1 W / (mK) in at least one direction at 25 degrees Celsius. Example 4. 4. The aerosol-generating article of example 3, wherein the aerosol-forming substrate further comprises 7-60% by weight of an aerosol former, 2-20% by weight of fibers, and 2-10% by weight of a binder. Example 5. The aerosol-generating article of example 3 or 4, wherein the aerosol-forming substrate has a thermal conductivity of at least 0.12 W / (mK), such as at least 0.14 W / (mK), such as at least 0.22 W / (mK), in at least one direction at 25 degrees Celsius. Example 6. 6. The aerosol-generating article of any one of Examples 1 to 5, wherein the aerosol-forming substrate comprises, on a dry weight basis, 10 to 90% by weight of thermally conductive particles, 7 to 60% by weight of an aerosol former, 2 to 20% by weight of fibers, and 2 to 10% by weight of a binder, and each of the thermally conductive particles is one or more of graphite, expanded graphite, graphene, carbon nanotubes, charcoal, and diamond. Example 7. An aerosol-generating article as described in any of Examples 1 to 6, wherein each of the plurality of thermally conductive particles has a thermal conductivity of at least 0.3, 0.5, 1, 2, 5, or 10 W / (mK) in at least one direction, for example, when measured at 25 degrees Celsius. Example 8. The aerosol-generating article of any of Examples 1-7, wherein some or all of the thermally conductive particles comprise carbon, e.g., at least 10, 30, 50, 70, 90, 95, 98, or 99% by weight carbon. Example 9. An aerosol-generating article as described in any of Examples 1 to 8, wherein some or all of the thermally conductive particles are graphite particles, or some or all of the thermally conductive particles are expanded graphite particles, or some of the thermally conductive particles are graphite particles and some of the thermally conductive particles are expanded graphite particles. Example 10. An aerosol-generating article as described in any one of Examples 1 to 9, wherein some or all of the thermally conductive particles are diamond particles, for example synthetic diamond particles. Example 11. An aerosol-generating article according to any one of Examples 1 to 10, wherein some or all of the thermally conductive particles are graphene particles. Example 12. An aerosol-generating article as described in any one of Examples 1 to 11, wherein some or all of the thermally conductive particles are carbon nanotubes. Example 13. An aerosol-generating article according to any one of Examples 1 to 12, wherein some or all of the thermally conductive particles are charcoal particles. Example 14. 14. The aerosol-generating article of any one of Examples 1 to 13, wherein some or all of the thermally conductive particles comprise a metal. Example 15. An aerosol-generating article according to any one of Examples 1 to 14, wherein some or all of the thermally conductive particles comprise one or both of copper and aluminum. Example 16. 16. An aerosol-generating article as described in any one of Examples 1 to 15, wherein some or all of the thermally conductive particles comprise an alloy. Example 17. 17. The aerosol-generating article of any one of Examples 1-16, wherein some or all of the thermally conductive particles comprise an intermetallic compound. Example 18. 18. An aerosol-generating article according to any one of Examples 1 to 17, wherein the thermally conductive particles have a particle size distribution with a particle size number D10, and the particle size number D10 is at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, or 500 microns. Example 19. 19. An aerosol-generating article according to any one of Examples 1 to 18, wherein the thermally conductive particles have a particle size distribution with a particle size number D10, and the particle size number D10 is less than 1,000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns. Example 20. 20. An aerosol-generating article according to any one of Examples 1 to 19, wherein the thermally conductive particles have a particle size distribution with a particle size number D50, and the particle size number D50 is at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, or 500 microns. Example 21. 21. An aerosol-generating article according to any one of Examples 1 to 20, wherein the thermally conductive particles have a particle size distribution with a particle size number D50, and the particle size number D50 is less than or equal to 1,000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns. Example 22. 22. An aerosol-generating article according to any one of Examples 1 to 21, wherein the thermally conductive particles have a particle size distribution with a particle size number D90, and the particle size number D90 is at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, or 500 microns. Example 23. 23. An aerosol-generating article as described in any one of Examples 1 to 22, wherein the thermally conductive particles have a particle size distribution having a particle size number D90, and the particle size number D90 is less than or equal to 1,000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns. Example 24. 24. An aerosol-generating article as described in any one of Examples 1 to 23, wherein the thermally conductive particles have a particle size distribution with a particle size in volume D10, and the particle size in volume D10 is at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, or 500 microns. Example 25. 25. An aerosol-generating article according to any one of Examples 1 to 24, wherein the thermally conductive particles have a particle size distribution with a particle size in volume D10 that is less than 1,000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns. Example 26. 26. The aerosol-generating article of any one of Examples 1-25, wherein the thermally conductive particles have a particle size distribution with a particle size by volume D50 of at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, or 500 microns. Example 27. 27. An aerosol-generating article as described in any one of Examples 1 to 26, wherein the thermally conductive particles have a particle size distribution with a particle size by volume D50 of less than or equal to 1,000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns. Example 28. 28. An aerosol-generating article according to any one of Examples 1 to 27, wherein the thermally conductive particles have a particle size distribution with a particle size by volume D90 of at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, or 500 microns. Example 29. 29. An aerosol-generating article according to any one of Examples 1 to 28, wherein the thermally conductive particles have a particle size distribution with a particle size by volume D90 of less than or equal to 1,000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns. Example 30. The aerosol-generating article of any one of Examples 1 to 29, wherein the thermally conductive particles have a particle size distribution having a particle size number D10, a particle size number D90, a volume D10 particle size, and a volume D90 particle size, and the particle size distribution of the particle size number D90 is 50, 40, 30, 20, 10, or 5 times the particle size number D10, or the particle size of the volume D10 is 50, 40, 30, 20, 10, or 5 times the particle size number D10, or both particle sizes of the number D90 are 50, 40, 30, 20, 10, or 5 times the particle size number D10 and the volume D10 particle size is 50, 40, 30, 20, 10, or 5 times the particle size number D10. Example 31. 31. An aerosol-generating article according to any one of Examples 1 to 30, wherein the thermally conductive particles have a particle size distribution, and one or both of the particle size number D10 and the particle size volume D10 are between 1 and 20 microns. Example 32. An aerosol-generating article as described in any one of Examples 1 to 31, wherein the thermally conductive particles have a particle size distribution, and one or both of the number D90 particle size and the volume D90 particle size are 50 to 300 microns, or 50 to 200 microns. Example 33. 33. The aerosol-generating article of any one of Examples 1-32, wherein each of the thermally conductive particles has a particle size of at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, or 500 microns. Example 34. 34. The aerosol-generating article of any one of Examples 1-33, wherein each of the thermally conductive particles has a particle size of less than 1,000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns. Example 35. An aerosol-generating article described in any of Examples 1 to 34, wherein each of the thermally conductive particles has three mutually perpendicular dimensions, and the largest dimension of the three dimensions is 10, 8, 5, 3, or 2 times greater than one or both of the smallest dimension of the three dimensions and the second largest dimension of the three dimensions. Example 36. An aerosol-generating article according to any one of Examples 1 to 35, wherein each of the thermally conductive particles is substantially spherical. Example 37. 37. The aerosol-generating article of any one of Examples 1-36, wherein the thermally conductive particles comprise at least 10, 20, 50, 100, 200, 500, or 1000 particles. Example 38. 38. The aerosol-generating article of any one of Examples 1-37, wherein the substrate comprises at least 20, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, or 85 weight percent of thermally conductive particles on a dry weight basis. Example 39. 39. The aerosol-generating article of any one of Examples 1-38, wherein the substrate comprises, on a dry weight basis, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, or 15% or less by weight of thermally conductive particles. Example 40. 40. The aerosol-generating article of any one of Examples 1-39, wherein the substrate comprises, on a dry weight basis, 10-90, 20-90, 30-90, 40-90, 50-90, 60-90, 70-90, 80-90, 10-80, 20-80, 30-80, 40-80, 50-80, 60-80, 70-80, 10-70, 20-70, 30-70, 40-70, 50-70, 60-70, 10-60, 20-60, 30-60, 40-60, 50-60, 10-50, 20-50, 30-50, 40-50, 10-40, 20-40, 30-40, 10-30, 20-30, or 10-20 weight percent of thermally conductive particles. Example 41. 41. The aerosol-generating article of any of Examples 1-40, wherein the substrate comprises at least 10, 15, 20, 25, 30, 35, 40, 45, 50, or 55% by weight of the aerosol former on a dry weight basis. Example 42. 42. The aerosol-generating article of any one of Examples 1-41, wherein the substrate comprises, on a dry weight basis, 55, 50, 45, 40, 35, 30, 25, 20, or 15% by weight or less of an aerosol former. Example 43. 43. The aerosol-generating article of any one of Examples 1 to 42, wherein the substrate comprises 7 to 60, 10 to 60, 20 to 60, 30 to 60, 40 to 60, 50 to 60, 7 to 50, 10 to 50, 20 to 50, 30 to 50, 40 to 50, 7 to 40, 10 to 40, 20 to 40, 30 to 40, 7 to 30, 10 to 30, 20 to 30, 7 to 20, 10 to 20, or 7 to 10 aerosol formers, particularly preferably 15 to 25 wt. % of aerosol formers, on a dry weight basis. Example 44. The aerosol-generating article of any one of Examples 1 to 43, wherein the aerosol former comprises or consists of one or more of polyhydric alcohols (such as propylene glycol, polyethylene glycol, triethylene glycol, 1,3-butanediol, and glycerin), esters of polyhydric alcohols (such as glycerol monotriacetate, glycerol diacetate, or glycerol triacetate), and aliphatic esters of mono-, di-, or polycarboxylic acids (such as dimethyl dodecanedioate and dimethyl tetradecanedioate). Example 45. The aerosol-generating article of any one of Examples 1 to 44, wherein the aerosol-forming substrate comprises one or both of glycerin and glycerol. Example 46. The aerosol-generating article of any one of Examples 1-45, wherein the substrate comprises at least 2, 4, 6, 8, 10, 12, 14, 16, or 18 weight percent fibers on a dry weight basis. Example 47. 47. The aerosol-generating article of any one of Examples 1-46, wherein the substrate comprises no more than 20, 18, 16, 14, 12, 10, 8, 6, or 4 weight percent fibers on a dry weight basis. Example 48. The substrates are, on a dry weight basis, 4-20, 6-20, 8-20, 10-20, 12-20, 14-20, 16-20, 18-20, 2-18, 4-18, 6-18, 8-18, 10-18, 12-18, 14-18, 16-18, 2-16, 4-16, 6-16, 8-16, 10-16, 12-16, 14-16, 2-14, 4-1 48. The aerosol-generating article of any of Examples 1-47, comprising 4, 6-14, 8-14, 10-14, 12-14, 2-12, 4-12, 6-12, 8-12, 10-12, 2-10, 4-10, 6-10, 8-10, 2-8, 4-8, 6-8, 2-6, 4-6, or 2-4 wt.% of fibers, preferably 2-10 wt.% of fibers. Example 49. The aerosol-generating article according to any one of Examples 1 to 48, wherein the fibers are cellulose fibers. Example 50. An aerosol-generating article described in any of Examples 1 to 49, wherein each of the fibers has three mutually perpendicular dimensions, and the largest of the three dimensions is at least 1.5, 2, 3, 5, 10, or 20 times greater than the smallest of the three dimensions. Example 51. An aerosol-generating article described in any of Examples 1 to 50, wherein each of the fibers has three mutually perpendicular dimensions, and the largest of the three dimensions is at least 1.5, 2, 3, 5, 10, or 20 times greater than the second largest of the three dimensions. Example 52. An aerosol-generating article according to any one of Examples 1 to 51, wherein the substrate comprises at least 4, 6, or 8% by weight of binder on a dry weight basis. Example 53. 53. The aerosol-generating article of any of Examples 1-52, wherein the substrate comprises no more than 8, 6, or 4 weight percent binder on a dry weight basis. Example 54. 54. The aerosol-generating article according to any one of Examples 1 to 53, wherein the substrate comprises, on a dry weight basis, 4 to 10, 6 to 10, 8 to 10, 2 to 8, 4 to 8, 6 to 8, 2 to 6, 4 to 6, 2 to 4 wt. % of binder, particularly preferably 2 to 10 wt. % of binder. Example 55. An aerosol-generating article according to any one of Examples 1 to 54, wherein the binder comprises or consists of one or both of carboxymethyl cellulose or hydroxypropyl cellulose. Example 56. 56. An aerosol-generating article according to any one of Examples 1 to 55, wherein the binder comprises or consists of one or more gums, such as guar gum. Example 57. An aerosol-generating article according to any one of Examples 1 to 56, wherein the thermally conductive particles are distributed substantially homogeneously throughout the aerosol-forming substrate. Example 58. The aerosol-generating article of any one of Examples 1 to 57, wherein the aerosol-forming body is substantially homogeneously distributed throughout the aerosol-forming substrate. Example 59. An aerosol-generating article according to any one of Examples 1 to 58, wherein the fibers are substantially homogeneously distributed throughout the aerosol-forming substrate. Example 60. An aerosol-generating article according to any one of Examples 1 to 59, wherein the binder is distributed substantially homogeneously throughout the aerosol-forming substrate. Example 61. The aerosol-generating article according to any one of Examples 1 to 60, wherein the substrate comprises nicotine. Example 62. 62. The aerosol-generating article of Example 61, wherein the substrate comprises at least 0.01, 1, 2, 3, or 4% nicotine by weight on a dry weight basis. Example 63. 63. The aerosol-generating article of any one of Examples 61-62, wherein the substrate comprises no more than 5, 4, 3, 2, or 1% nicotine by weight on a dry weight basis. Example 64. 64. An aerosol-generating article according to any one of Examples 1 to 63, wherein the substrate contains, on a dry weight basis, 0.01 to 5, 1 to 5, 2 to 5, 3 to 5, 4 to 5, 0.01 to 4, 1 to 4, 2 to 4, 3 to 4, 0.01 to 3, 1 to 3, 2 to 3, 0.01 to 2, 1 to 2, 0.01 to 1% by weight of nicotine, particularly preferably 0.5 to 4% by weight of nicotine. Example 65. An aerosol-generating article according to any one of Examples 61 to 63, wherein the nicotine is distributed substantially homogeneously throughout the aerosol-forming substrate. Example 66. The aerosol-generating article of any one of Examples 1 to 65, wherein the substrate comprises an acid. Example 67. 67. The aerosol-generating article of Example 66, wherein the substrate comprises at least 0.01, 1, or 2 weight percent acid on a dry weight basis. Example 68. 68. The aerosol-generating article of any one of Examples 66-67, wherein the substrate comprises, on a dry weight basis, no more than 3, 2, or 1 weight percent acid. Example 69. 69. The aerosol-generating article of any one of Examples 66 to 68, wherein the substrate comprises, on a dry weight basis, 0.01 to 3, 1 to 3, 2 to 3, 0.01 to 2, 1 to 2, or 0.01 to 1 wt. % of acid, particularly preferably 0.5 to 5 wt. % of acid. Example 70. 70. The aerosol-generating article of any one of Examples 66 to 69, wherein the acid comprises or consists of one or more of fumaric acid, lactic acid, benzoic acid, and levulinic acid. Example 71. 71. The aerosol-generating article of any one of Examples 66-70, wherein the acid is distributed substantially homogeneously throughout the aerosol-forming substrate. Example 72. The aerosol-generating article of any one of Examples 1 to 71, wherein the substrate comprises at least one plant. Example 73. The aerosol-generating article of Example 72, wherein the substrate comprises at least 0.01, 1, 2, 5, 10, or 15% by weight of at least one plant on a dry weight basis. Example 74. 74. The aerosol-generating article of any one of Examples 72-73, wherein the substrate comprises, on a dry weight basis, no more than 20, 15, 10, 5, 2, or 1 weight percent of at least one plant. Example 75. 75. The aerosol-generating article of any of Examples 72 to 74, wherein the substrate comprises, on a dry weight basis, 0.01 to 20, 1 to 20, 2 to 20, 5 to 20, 10 to 20, 15 to 20, 0.01 to 15, 1 to 15, 2 to 15, 5 to 15, 10 to 15, 0.01 to 10, 1 to 10, 2 to 10, 5 to 10, 0.01 to 5, 1 to 5, 2 to 5, 0.01 to 2, 1 to 2, or 0.01 to 1% by weight of at least one plant, particularly preferably 1 to 15% by weight of at least one plant. Example 76. An aerosol-generating article according to any one of Examples 72 to 75, wherein the at least one plant comprises or consists of one or both of clove and rosmanus. Example 77. The aerosol-generating article of any one of Examples 72 to 76, wherein the at least one plant is substantially uniformly distributed throughout the aerosol-forming substrate. Example 78. An aerosol-generating article according to any one of Examples 1 to 77, wherein the substrate comprises at least one flavorant. Example 79. 79. The aerosol-generating article of Example 78, wherein the substrate comprises at least 0.1, 1, 2, or 5% by weight, on a dry weight basis, of at least one flavorant. Example 80. 80. An aerosol-generating article according to any one of Examples 78-79, wherein the substrate comprises, on a dry weight basis, 10, 5, 2, or 1 weight percent or less of at least one flavoring agent. Example 81. 81. The aerosol-generating article of any of Examples 78 to 80, wherein the substrate comprises, on a dry weight basis, 0.1 to 10, 1 to 10, 2 to 10, 5 to 10, 0.1 to 5, 1 to 5, 2 to 5, 0.1 to 2, 1 to 2, or 0.1 to 1% by weight of at least one flavorant, particularly preferably 0.1 to 5% by weight of at least one flavorant. Example 82. An aerosol-generating article according to any of Examples 78 to 81, wherein the at least one flavorant is present as a coating, for example a coating on one or more other components of the aerosol-forming substrate. Example 83. An aerosol-generating article according to any one of Examples 78 to 82, wherein the at least one flavoring agent is substantially homogeneously distributed throughout the aerosol-forming substrate. Example 84. The aerosol-generating article of any one of Examples 1-83, wherein the aerosol-forming substrate comprises one or more organic materials, such as tobacco. Example 85. The aerosol-generating article of any one of Examples 1 to 84, wherein the organic material comprises one or more of herb leaves, tobacco leaves, tobacco stem fragments, reconstituted tobacco, homogenized tobacco, extruded tobacco, and expanded tobacco. Example 86. The aerosol-generating article of any one of Examples 1-85, wherein the organic material is substantially homogeneously distributed throughout the aerosol-forming substrate. Example 87. The aerosol-forming substrate is an aerosol-forming substrate that does not contain tobacco, for example, the aerosol-generating article according to any one of Examples 1 to 86, wherein the aerosol-forming substrate does not contain tobacco. Example 88. The aerosol-generating article of any of Examples 1-87, wherein some or each of the thermally conductive particles comprises and / or is formed from a susceptor material, e.g., a carbon susceptor material. Example 89. An aerosol-generating article according to any one of Examples 1 to 88, wherein the aerosol-forming substrate has a thermal conductivity of at least 0.15, 0.2, 0.22, 0.3, 0.4, 0.5, 0.75, 1, 1.25, or 1.5 W / (mK) in at least one direction, or in all directions, at 25 degrees Celsius. Example 90. 90. The aerosol-generating article of any one of Examples 1 to 89, wherein the aerosol-forming substrate has a density of less than 1500, 1050, 1000, 950, 900, 850, 800, 850, 800, 750, 700, or 650 kg / m3. Example 91. The aerosol-forming substrate is 500 to 900 kg / m 3 , or 600-800kg / m 3 91. The aerosol-generating article of any one of Examples 1 to 90, having a density of Example 92. 92. The aerosol-generating article of any of Examples 1-91, wherein the aerosol-forming substrate has a moisture content of 1 to 20, or 3 to 15 wt. %. Example 93. 93. The aerosol-generating article of any one of Examples 1 to 92, wherein the aerosol-forming substrate comprises 1 to 20, or 3 to 15 wt. % water. Example 94. The aerosol-forming substrate has a mass of at least 0.1, 0.2, 0.3, or 0.5 g / m 3 The aerosol-generating article of any one of Examples 1 to 93, having a density of Example 95. The aerosol-forming substrate has a density of at least 2, 1.5, 1.2, or 1 g / m 3 The aerosol-generating article of any one of Examples 1 to 94, having a density of Example 96. The aerosol-forming substrate is 0.1 to 2 g / m 2 , 0.2~2g / m 2 , 0.3~2g / m 2 , 0.3~1.5g / m 2 , or 0.3 to 1.2 g / m 3 The aerosol-generating article of any one of Examples 1 to 95, having a density of Example 97. 97. The aerosol-generating article of any of Examples 1 to 96, wherein the substrate is in the form of a tube having a width in the radial dimension and a length in the longitudinal dimension, the length being 5 mm to 100 mm, for example, 6 mm to 80 mm, for example, 7 mm to 60 mm, for example, 8 mm to 55 mm, for example, 9 mm to 50 mm, for example, 10 mm to 45 mm, for example, 11 mm to 35 mm, for example, 12 mm to 25 mm. Example 98. An aerosol-generating article according to any of Examples 1 to 97, wherein the substrate is in the form of a tube having a width in the radial dimension and a length in the longitudinal dimension, the width being defined by the outer diameter of the tube, the outer diameter being from 3mm to 20mm, for example, from 4mm to 12mm, such as from 4.5mm to 10mm, for example, from 5mm to 9mm, such as from 6mm to 8mm, for example, from 6.5mm to 7.5mm, for example, about 7mm. Example 99. 99. The aerosol-generating article of any of Examples 1 to 98, wherein the substrate is in the form of a tube having an outer diameter and an inner diameter, the inner diameter being from 2.5 mm to 19 mm, for example, from 3.5 mm to 11.5 mm, for example, from 4 mm to 9 mm, for example, from 4.5 mm to 8.5 mm, for example, from 5.5 mm to 7.5 mm, for example, from 6.9 mm to 7.3 mm, for example, about 7 mm. Example 100. 99. An aerosol-generating article according to any of Examples 1 to 99, wherein the substrate is in the form of a tube having a length, an outer diameter and an inner diameter, a wall thickness of the tube defined by the difference between the outer and inner diameters, and the wall thickness is from 100 microns to 5 mm, such as from 150 microns to 3 mm, for example from 200 microns to 2 mm, for example from 250 microns to 1.5 mm, such as from 300 microns to 1 mm, for example from 350 microns to 500 microns. Example 101. The aerosol-generating article of any of Examples 1-100, wherein the substrate is in the form of a tube, and the tube is a rolled sheet of aerosol-forming material, e.g., a rolled sheet of homogenized tobacco material, e.g., a rolled sheet of cast leaf tobacco, or, e.g., a rolled sheet of tobacco-free aerosol-forming material. Example 102. The aerosol-generating article of any of Examples i-100, wherein the substrate is in the form of a tube, and the tube is an extruded tube of aerosol-forming material, such as an extruded tube of homogenized tobacco material, or, for example, an extruded tube of aerosol-forming material that does not include tobacco. Example 103. An aerosol-generating article as described in any of Examples 1-102, wherein the aerosol-generating article comprises a front plug, for example the front plug has a length of 2 mm to 10 mm, 3 mm to 8 mm, or 4 mm to 6 mm, for example about 5 mm. Example 104. The aerosol-generating article of any of Examples 1-103, wherein the aerosol-generating article comprises a first hollow support tube, e.g., a first hollow acetate tube, e.g., the first hollow support tube is located downstream of the aerosol-forming substrate within the aerosol-generating article. Example 105. The aerosol-generating article of any of Examples 1-104, wherein the aerosol-generating article comprises a second hollow support tube, e.g., a second hollow acetate tube, e.g., the second hollow support tube is located downstream of the aerosol-forming substrate within the aerosol-generating article. Example 106. The aerosol-generating article of example 105, wherein the second hollow support tube comprises one or more vent holes. Example 107. The aerosol-generating article according to any one of Examples 1 to 106, comprising a mouth-side plug filter. Example 108. An aerosol-generating article according to any one of Examples 1 to 107, wherein the aerosol-generating article comprises a wrapper, e.g., a paper wrapper, and the components of the aerosol-generating article including, e.g., the aerosol-forming substrate, are assembled within the wrapper. Example 109. The aerosol-generating article according to any one of Examples 1 to 108, comprising a front plug, wherein the aerosol-forming substrate is disposed downstream of the front plug, a first hollow support tube disposed downstream of the aerosol-forming substrate, a second hollow support tube disposed downstream of the first hollow support tube, and a mouth-side plug filter disposed downstream of the second hollow support tube, preferably wherein the front plug, the aerosol-forming substrate, the first hollow support tube, the second hollow support tube and the mouth-side plug filter are surrounded by a wrapper, for example a paper wrapper. Example 110. The aerosol-generating article according to any one of Examples 1 to 109, wherein the aerosol-forming substrate has a length of 5 mm to 30 mm. Example 111. The aerosol-generating article according to any one of Examples 1 to 110, wherein the aerosol-forming substrate has a length of 5 mm to 16 mm. Example 112. An aerosol-generating article according to any one of Examples 1 to 111, wherein the wall thickness of the aerosol-forming substrate is between 5 percent and 40 percent of the outer diameter of the aerosol-forming substrate. Example 113. A method of forming a hollow tubular aerosol-forming substrate for an aerosol-generating article, such as an aerosol-generating article as defined by any of Examples i to 112, comprising the steps of: forming a slurry including thermally conductive particles, an aerosol former, fibers, and a binder; A method comprising: casting the slurry into the shape of a hollow tubular aerosol-forming substrate to form a hollow tubular aerosol-forming substrate; and drying the cast slurry. Example 114. A method of forming a hollow tubular aerosol-forming substrate for an aerosol-generating article, such as an aerosol-generating article as defined by any of Examples i to 112, comprising the steps of: forming a slurry including thermally conductive particles, an aerosol former, fibers, and a binder; A method comprising extruding the slurry into the shape of a hollow tubular aerosol-forming substrate, and drying the extruded slurry into the hollow tube. Example 115. The method of example 114, further comprising the step of cutting the hollow tube to form a hollow tubular aerosol-forming substrate. Example 116. A method of forming a hollow tubular aerosol-forming substrate for an aerosol-generating article, such as an aerosol-generating article as defined by any of Examples i to 112, comprising the steps of: forming a slurry including thermally conductive particles, an aerosol former, fibers, and a binder; A method comprising casting and drying the slurry to form a sheet of aerosol-forming material, and forming the sheet into a hollow tube. Example 117. The method of example 116, further comprising the step of cutting the hollow tube to form a hollow tubular aerosol-forming substrate. Example 118. The method of example 116 or 117, wherein forming the sheet into a hollow tube includes rolling the sheet into a tubular shape and applying an adhesive to overlapping ports of the rolled sheet to maintain the rolled sheet in the tubular shape. Example 119. The method of any one of Examples 113 to 118, wherein the slurry comprises water. Example 120. The method according to any one of Examples 113 to 119, wherein the slurry comprises 40-90%, 40-85%, 50-80%, 60-80%, or 60-75% by weight of water. Example 121. 121. The method of any of embodiments 113-120, wherein the slurry comprises an acid, such as fumaric acid. Example 122. The method of any one of Examples 113 to 121, wherein the slurry comprises nicotine. Example 123. Forming the slurry comprises: an aerosol former; Fibers and Water, Optionally, an acid, forming a first mixture comprising, optionally, nicotine; Thermally conductive particles; forming a second mixture comprising: The method of any of Examples 113-122, comprising adding the second mixture to the first mixture to form a combined mixture. Example 124. The method of example 123, wherein forming the first mixture includes providing an aerosol former, or a solution including an aerosol former and nicotine. Example 125. The method of example 124, wherein forming the first mixture includes adding an acid to the aerosol former, or a solution containing the aerosol former and nicotine, to form a first premixture. Example 126. The method of any of Examples 123-125, wherein forming the first mixture includes adding water to the aerosol former, or to a solution comprising the aerosol former and nicotine, or to the first premix to form a second premix. Example 127. The method of example 126, wherein forming the first mixture includes adding fibers to the second premix. Example 128. 128. The method of any of Examples 126-127, wherein forming the second mixture includes mixing thermally conductive particles and a binder. Example 129. The method of any of Examples 126-128, wherein the method comprises first mixing the combined mixtures. Example 130. 130. The method of example 129, wherein the first mixing is performed under a first pressure of less than or equal to 500, 400, 300, 250, or 200 mbar. Example 131. The method of any one of Examples 129 and 130, wherein the first mixing is carried out for 1 to 10 minutes, 2 to 8 minutes, or 3 to 6 minutes, for example, about 4 minutes. Example 132. The method of any of Examples 129-131, wherein the method includes, after the first mixing, a second mixing. Example 133. 133. The method of embodiment 132, wherein the second mixing is conducted under a second pressure that is less than the first pressure. Example 134. The method of example 133, wherein the second pressure is less than or equal to 500, 400, 300, 200, 150, or 100 mbar. Example 135. The method of example 132 or 133 or 134, wherein the second mixing is carried out for 5 to 120 seconds, 5 to 80 seconds, 5 to 40 seconds, or 10 to 30 seconds, for example, for about 20 seconds. Example 136. 136. The method of any of Examples 116-135, wherein casting the slurry includes casting the slurry onto a flat support, such as a steel flat support. Example 137. The method of any of Examples 113-136, wherein after casting the slurry and before drying the slurry, the method comprises setting a thickness of the slurry, e.g., setting a thickness of the slurry to 100-1,000 microns, 200-900 microns, 300-800, 500-700 microns, e.g., about 600 microns. Example 138. The method of any of Examples 113-137, wherein drying the slurry comprises providing a flow of gas, such as air, over or through the slurry. Example 139. The method of embodiment 138, wherein the gas stream is heated. Example 140. 139. The method of claim 139, wherein the gas stream is heated to a temperature of 100 to 160 degrees Celsius, or 120 to 140 degrees Celsius. Example 141. The method of any of Examples 138-140, wherein the flow of gas is provided for 1 to 10 minutes or 2 to 5 minutes. Example 142. 142. The method of any of Examples 113-141, wherein drying the slurry includes drying the slurry until the slurry has a moisture content of 1-20, 2-15, 2-10, or 3-7 wt.%. Example 143. The method of any of examples 113-142, wherein drying the slurry forms a precursor for formation into an aerosol-forming substrate, the precursor being a sheet of aerosol-forming material. Example 144. An aerosol generating system comprising the aerosol-generating article according to any one of Examples i to 112 and an electrical aerosol generating device. Example 145. An aerosol generating system as described in Example 144, wherein the electrical aerosol generating device is configured to resistively heat the aerosol generating article during use. Example 146. 146. An aerosol generating system according to any one of Examples 144 to 145, wherein the electrical aerosol generating device is configured, in use, to inductively heat an aerosol-generating article, such as an aerosol-forming substrate of the aerosol-generating article.

[0134] The embodiments will now be further described with reference to the following figures:

[0135] 1 shows a schematic cross-sectional view of an exemplary aerosol-generating article 10 according to one embodiment of the present invention. The aerosol-generating article 10 extends from an upstream or distal end 18 to a downstream or proximal or mouth end 20 and has an overall length of about 45 millimeters and a diameter of about 7.2 mm.

[0136] The aerosol-generating article 10 comprises multiple elements arranged coaxially and assembled within a wrapper 70. The multiple elements forming the article are, from distal to proximal end, a front plug 46, a tubular segment of thermally enhanced aerosol-forming substrate 12, a cardboard tube-free flow filter 34, and a mouthpiece filter 42. The wrapper 70 may be a cigarette paper.

[0137] The front plug 46, also referred to as the upstream element, is located immediately upstream of the tubular aerosol-forming substrate 12. The upstream element 46 is provided in the form of a cylindrical plug of cellulose acetate. The front plug 46 has a diameter of about 7.2 mm and a length of about 5 mm. The RTD of the front plug 46 is about 30 mm HO.

[0138] The tubular segment of the aerosol-forming substrate 12 has an outer diameter of about 7.2 millimeters, an inner diameter of about 6.8 millimeters, and a length of about 12 millimeters. The aerosol-forming substrate 12 is formed from a rolled sheet of an aerosol-forming material that includes thermally conductive particles 44. The tubular aerosol-forming substrate 12 is configured to form an aerosol when heated to a temperature of between 150 degrees Celsius and 350 degrees Celsius. Some specific examples of suitable aerosol-forming substrate compositions are provided below.

[0139] The cardboard tube 34 has a length of 16 mm and provides free space within the article 10 in which the volatile components generated by heating the aerosol-forming substrate can cool and form an aerosol.

[0140] The mouthpiece element 42 is provided in the form of a cylindrical plug of low density cellulose acetate. The mouthpiece element 42 has a length of about 12 millimeters and an outside diameter of about 7.2 mm. The RTD of the mouthpiece element 42 is about 12 millimeters HO.

[0141] It should be apparent that the configuration of the aerosol-generating article 10 in Figure 1 is intended to serve as an example only: the thermally enhanced tubular aerosol-forming substrate 12 may, for example, be used in aerosol-generating articles that are longer, e.g., 80 mm in length, and thinner, e.g., 4.5 mm in diameter.

[0142] In a particular embodiment of the aerosol-generating article shown in Figure 1, the tubular segment 12 of the aerosol-forming substrate comprises about 76.1% by weight of thermally conductive particles 44 on a dry weight basis. In this embodiment, the thermally conductive particles 44 are graphite particles, specifically AMG Graphite GK FP 99.5 (>99.5% purity) graphite particles from Graphit Kropfmul GmbH, although other particles or mixtures of particles may be used. Each thermally conductive particle has a thermal conductivity of about 6 W / (mK) in at least one direction at 25 degrees Celsius.

[0143] The tubular aerosol-forming substrate 12 comprises, on a dry weight basis, about 17.7% by weight of an aerosol former, in this embodiment, the aerosol former is glycerol, in particular ICOF European food grade (>99.5% purity) glycerol.

[0144] The tubular aerosol-forming substrate 12 comprises, on a dry weight basis, about 3.9% by weight of fibres, in this embodiment the fibres being cellulose fibres, in particular birch cellulose fibres from Stora Enso OYJ.

[0145] The tubular aerosol-forming substrate 12 comprises about 2.3% by weight of a binder on a dry weight basis. In this embodiment, the binder is guar gum, in particular guar gum from Gumix International Inc.

[0146] The tubular aerosol-forming substrate contains about 10% water by weight when measured at 25 degrees Celsius.

[0147] In other embodiments, the tubular aerosol-forming substrate 12 further comprises one or more of nicotine, an acid such as fumaric acid, a botanical such as clove or rosmarinus, and a flavoring agent.

[0148] The tubular aerosol-forming substrate 12 has a thermal conductivity of at least 0.1 W / (mK) in at least one direction at 25 degrees Celsius. The aerosol-forming substrate 12 may have a thermal conductivity of 0.2, 0.5, 1, 1.5 or more W / (mK) in at least one direction at 25 degrees Celsius.

[0149] Each of the thermally conductive particles 44 is substantially spherical in shape. The thermally conductive particles 44 are substantially homogeneously distributed throughout the aerosol-forming substrate. The particle size distribution has a volume D10 particle size of about 6 microns, a volume D50 particle size of about 20 microns, and a volume D90 particle size of about 56 microns. Each of the thermally conductive particles 44 has a particle size greater than about 1 micron and less than about 300 microns.

[0150] The thermally conductive particles 44 have a density of about 2200 kilograms per cubic meter. The aerosol-forming substrate has a density of about 800 kilograms per cubic meter.

[0151] The aerosol-forming substrate is formed by the process described below.

[0152] The slurry is formed using a laboratory sparser, which has the ability to mix viscous liquids, disperse powders through liquids, and remove gas from the mixture (e.g., by applying a vacuum or other suitably low pressure). In this embodiment, a laboratory sparser commercially available from PC Laborsystem was used.

[0153] To form a slurry, a first mixture is formed by adding about 7.11 grams of aerosol former, then about 157.5 grams of water, then about 1.57 grams of fiber to a lab dispenser. These first components are then mixed at 600-700 rpm for 5 minutes at 25 degrees Celsius to ensure a homogenous mixture and to hydrate the fiber. A second mixture is then formed by manually mixing about 32.95 grams of thermally conductive particles and about 0.92 grams of binder. This mixing of the second mixture avoids the formation of lumps in the lab dispersion. The second mixture is then added to the first mixture to form a combined mixture. The combined mixture is then mixed at 5000 rpm for 4 minutes at 25 degrees Celsius and a first reduced pressure of about 200 mbar. The reduced pressure can help ensure that the thermally conductive particles are homogenously dispersed in the mixture and that there is little trapped air and few lumps in the combined mixture. The combined mixture is then mixed at 5000 rpm for 20 seconds under a second vacuum of 25 degrees Celsius and about 100 mbar. This second vacuum can help remove any remaining air bubbles. This forms a slurry for molding.

[0154] The slurry is then cast and dried using a suitable apparatus, in this embodiment a commercially available Labcoater Mathis apparatus is used, which includes a stainless steel, flat support, and a caster blade to control the thickness of the cast slurry on the flat support.

[0155] The slurry is cast onto a flat support and the gap between the caster blade and the flat support is set at 0.6 millimeters, ensuring that the thickness of the slurry is no more than 0.6 millimeters at any given point.

[0156] The slurry is then dried with hot air at 120-140 degrees Celsius for 2-5 minutes. After this drying, a sheet of aerosol-forming substrate is formed. The sheet has a thickness of about 300 microns, a basis weight of about 250 grams per square meter, and a density of about 0.79 kilograms per cubic meter.

[0157] The sheet is then rolled to form a tube. Adhesive is applied to the overlapping portions of the rolled sheet to attach the sheet in the form of a tube, which is then cut to a length of 12 mm for the tubular aerosol-forming substrate 12.

[0158] After forming the tubular aerosol-forming substrate 12 , the aerosol-generating article 10 is assembled by positioning the various components of the article 10 and wrapping the components within a wrapper 70 .

[0159] Other embodiments may have the same structure as described above, but may have aerosol-forming substrates of different compositions. For example, in a further embodiment, the aerosol-forming material comprises a thermally enhanced homogenized tobacco tube comprising thermally conductive particles 44. The thermally conductive particles 44 are carbon particles, specifically expanded graphite particles, having a particle size distribution with a D10 particle size of 6.6 micrometers, a D50 particle size of 20 micrometers, and a D90 particle size of 56 micrometers. Each of the expanded graphite particles has a particle size greater than 2 microns and less than 100 microns. The expanded graphite particles have a volume average particle size of about 35 microns. Each of the expanded graphite particles is substantially spherical in shape. The expanded graphite particles have a density less than 1000 kilograms per cubic meter. The aerosol-forming substrate comprising the aerosol-forming material and the thermally conductive particles 44 has a combined density of about 760 kilograms per cubic meter. The expanded graphite particles constitute approximately 5% by weight of the aerosol-forming substrate.

[0160] The aerosol-forming substrate tube 12 is formed by a process which includes the following steps: premixing a binder, guar gum, with an aerosol former, glycerin, to form a first premix; premixing the fine cut tobacco material with a powder of expanded graphite particles 44 having a bulk density of about 0.065 grams per cubic centimeter to form a second premix; mixing the first and second premixes with water to form a slurry; Using a high shear mixer to homogenize the slurry; Casting the slurry onto a conveyor belt; controlling the thickness of the slurry and drying the slurry to form a sheet of the aerosol-forming substrate; and · Winding a sheet of the aerosol-forming substrate onto a tube and cutting the tube to form a tubular segment of the aerosol-forming substrate.

[0161] Aerosol-forming substrates formed with compositions including electrically conductive particles according to the present invention demonstrated improved aerosol delivery compared to a reference substrate that did not include thermally conductive particles.

[0162] 2 shows a schematic cross-sectional view of a first embodiment of an aerosol generating system 100. The system 100 comprises an aerosol generating device 102 and the aerosol-generating article 10 of FIG.

[0163] The aerosol generating device 102 comprises a battery 104, a controller 106, a heating blade 108 coupled to the battery, and a smoke detection mechanism (not shown). The controller 106 is coupled to the battery 104, the heating blade 108, and the smoke detection mechanism.

[0164] The aerosol generating device 102 further comprises a housing 110 defining a substantially cylindrical cavity for receiving a portion of the article 10. The heating blade 108 is centrally positioned within the cavity and extends longitudinally from the base of the cavity.

[0165] In this embodiment, the heating blade 108 comprises a substrate and an electrically resistive track located on the substrate. The battery 104 is coupled to the heating blade 108 such that a current can be applied to the electrically resistive track to heat the electrically resistive track and the heating blade 108 to an operating temperature.

[0166] In use, a user inserts the article 10 into the cavity and causes the heating blade 108 to extend through the upstream element 46 and into the internal bore or cavity of the tubular aerosol-forming substrate 12 of the article 10. Figure 3 shows the article 10 inserted into the cavity of the device 102 and the heating blade extending into the internal bore of the tubular aerosol-forming substrate.

[0167] The user then takes a puff on the downstream end of the article 10. This causes air to flow through an air inlet (not shown) of the device 102, and then through the article 10, from the upstream end 18 to the downstream end 20, and into the user's mouth.

[0168] When a user puffs on the article 10, air flows through the air inlet of the device. The puff detection mechanism detects when the airflow rate through the air inlet increases above a non-zero threshold flow rate. In response, the puff detection mechanism sends a signal to the controller 106. The controller 106 then controls the battery 104 to pass an electric current through the electrically resistive track, heating the heating blade 108. This heats up the tubular aerosol-forming substrate.

[0169] The thermally conductive particles 44 have a significantly higher thermal conductivity than the surrounding aerosol-forming material. These particles can therefore act as local hot spots and provide a more uniform temperature throughout the aerosol-forming substrate, especially in the radial direction from the heating blade 108, whereas in prior art substrates there can be significant temperature gradients. Furthermore, because the aerosol-forming substrate is in the form of a tube, the temperature equalizes relatively quickly between the inner and outer surfaces of the tube. The combination of the tubular structure for the aerosol-forming substrate and the presence of thermally conductive particles in the aerosol-forming substrate allows a larger proportion of the aerosol-forming substrate to quickly reach a temperature high enough to release volatile compounds, thus allowing a higher efficiency of use of the aerosol-forming substrate.

[0170] Heating of the aerosol-forming substrate causes it to release volatile compounds. These compounds are entrained in the air flowing from the upstream end 18 of the article 10 toward the downstream end 20 of the article 10. The compounds cool and condense to form an aerosol as it passes through the cardboard tube 34. The aerosol then passes through the mouthpiece element 42, which may remove undesirable particles that may be entrained in the airflow and enter the user's mouth.

[0171] When the user stops inhaling on the article 10, the airflow rate through the air inlet of the device decreases below a non-zero threshold flow rate. This is detected by the puff detection mechanism, which in response sends a signal to the controller 106. The controller 106 then controls the battery 104 to reduce the current passing through the electrically resistive track to zero.

[0172] After taking several puffs from the article 10, the user may choose to replace the article 10 with a new article.

[0173] 3 shows a schematic cross-sectional view of a second embodiment of an aerosol generating system 300. System 300 comprises an aerosol generating device 302 and the aerosol-generating article 10 of FIG.

[0174] The aerosol generating device 302 includes a battery 304, a controller 306, an external resistive heater 308, and a puff detection mechanism (not shown). The controller 306 is coupled to the battery 304, the resistive heater 308, and the puff detection mechanism.

[0175] The aerosol generating device 302 further comprises a housing 310 defining a substantially cylindrical cavity for receiving a portion of the article 10. The external heater 208 is located on an interior surface of the cavity.

[0176] Use of the system is similar to that described above in relation to the system of Figure 2, with the difference that the tubular aerosol-forming substrate 12 is heated externally rather than by a heater located within the interior portion of the aerosol-forming substrate.

[0177] 4 shows a schematic cross-sectional view of a third embodiment of an aerosol generating system 400. System 400 comprises an aerosol generating device 402 and the aerosol-generating article 10 of FIG.

[0178] The aerosol generating device 402 includes a battery 404, a controller 406, an inductor coil 408, and a puff detection mechanism (not shown). The controller 406 is coupled to the battery 404, the inductor coil 408, and the puff detection mechanism.

[0179] The aerosol generating device 402 further comprises a housing 410 defining a substantially cylindrical cavity for receiving a portion of the article 10. An inductor coil 408 spirals around the cavity.

[0180] The battery 404 is coupled to the inductor coil 408 such that an alternating current can be applied to the inductor coil 408 .

[0181] In use, a user inserts the article 10 into the cavity. Figure 4 shows the article 10 inserted into the cavity of the device 402. Airflow is detected and the device operates as described above in relation to the system of Figure 1. If a puff is detected, the controller 406 controls the battery 404 to pass an alternating current through the inductor coil 408. This causes the inductor coil 408 to generate a varying electromagnetic field. The aerosol-forming substrate 12 is located within this varying electromagnetic field. The material of the particles 44, for example graphite or expanded graphite, is a susceptor material. The varying electromagnetic field therefore generates eddy currents in the particles 44. This causes the particles 44 to heat up, which in turn heats up the aerosol-forming material of the aerosol-forming substrate.

[0182] For the purposes of this specification and the appended claims, unless otherwise indicated, all numbers expressing amounts, quantities, percentages, and the like should be understood in all cases as being modified by the term "about." Also, all ranges include the maximum and minimum points disclosed, and include any intermediate ranges therein, which may or may not be specifically recited herein. Thus, in this context, the number A is understood as A±10% of A. Within this context, the number A may be considered to include a numerical value that is within the general standard error for the measurement of the property that the number A modifies. The number A may deviate by the percentages recited above, in some cases as used in the appended claims, provided that the amount by which A deviates does not materially affect the basic and novel properties of the claimed invention. Also, all ranges include the maximum and minimum points disclosed, and include any intermediate ranges therein, which may or may not be specifically recited herein.

Claims

**Claim 1** An aerosol-generating article for generating an inhalable aerosol upon heating, comprising a plurality of components including an aerosol-forming substrate, wherein the aerosol-forming substrate is in the form of a hollow tubular segment defining a substrate recess extending between an upstream end and a downstream end of the aerosol-forming substrate, and the aerosol-forming substrate comprises a plurality of thermally conductive particles and an aerosol-forming material, the aerosol-generating article. **Claim 2** The aerosol-forming substrate according to claim 1, wherein the aerosol-forming substrate contains 5 to 95% by weight of thermally conductive particles on a dry weight basis, and each thermally conductive particle of the thermally conductive particles has a thermal conductivity of at least 1 W / (mK) in at least one direction at 25° C. **Claim 3** The aerosol-generating article according to claim 1 or 2, wherein the aerosol-forming substrate has a thermal conductivity of at least 0.12 W / (mK) in at least one direction at 25° C. **Claim 4** The aerosol-generating article according to claim 1 or 2, wherein each of the thermally conductive particles consists of one or more of graphite, expanded graphite, graphene, carbon nanotubes, charcoal, and diamond. **Claim 5** The aerosol-forming substrate contains, on a dry weight basis, 10 to 90% by weight of thermally conductive particles, 7 to 60% by weight of an aerosol-forming material, 2 to 20% by weight of fibers, and 2 to 10% by weight of a binder, and each of the thermally conductive particles consists of one or more of graphite, expanded graphite, graphene, carbon nanotubes, charcoal, and diamond. The aerosol-generating article according to claim 1 or 2. **Claim 6** The aerosol-generating article according to claim 1 or 2, wherein the thermally conductive particles are distributed substantially homogeneously throughout the aerosol-forming substrate. **Claim 7** The aerosol-generating article according to claim 1 or 2, wherein the aerosol-forming substrate contains one or more organic materials such as tobacco. **Claim 8** The aerosol-generating article according to claim 1 or 2, wherein the aerosol-forming substrate is an aerosol-forming substrate that does not contain tobacco. **Claim 9** The aerosol-forming substrate is in the form of a tube having an outer diameter, an inner diameter, and a length, the length of the tube is 5 mm to 100 mm, the outer diameter is 3 mm to 20 mm, and the inner diameter is 2.5 mm to 19.5 mm. The aerosol-generating article according to claim 1 or 2. **Claim 10** The length of the tube is 8 mm to 25 mm, the outer diameter of the tube is 6 mm to 8 mm, and the inner diameter of the tube is 5 mm to 7.9 mm. The aerosol-generating article according to claim 9.

11. The aerosol-generating article according to claim 1 or 2, wherein the hollow tubular segment is a wound sheet of aerosol-forming material.

12. The aerosol-generating article according to claim 1 or 2, wherein the hollow tubular segment is an extruded tube of aerosol-forming material.

13. A method of forming a hollow tubular aerosol-forming substrate for an aerosol-generating article, comprising: forming a slurry comprising thermally conductive particles, an aerosol former, fibers, and a binder; molding and drying the slurry to form a sheet of aerosol-forming material; and forming the sheet into a hollow tube.

14. Forming the slurry comprises: forming a first mixture comprising the aerosol former, the fibers, water, optionally an acid, and optionally nicotine; forming a second mixture comprising the thermally conductive particles and the binder; and adding the second mixture to the first mixture to form a combined mixture. The method according to claim 13.

15. An aerosol-generating system comprising the aerosol-generating article according to claim 1 or 2 and an electric aerosol-generating device, wherein the electric aerosol-generating device is configured to resistively heat the aerosol-generating article during use or the electric aerosol-generating device is configured to inductively heat the aerosol-generating article during use. ​

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