Auxetic outsole

Abstract

An auxetic outsole 100 for footwear comprising an integrally formed sole unit. The sole unit comprising a plurality of auxetic cavities 120, some of which intersect the periphery 130 of the sole and e

Description

TECHNICAL FIELD The present disclosure relates to an auxetic outsole. Particularly, the disclosure relates to an auxetic outsole with a plurality of cavities. Aspects of the invention relate to an auxetic outsole for an article of footwear, an article of footwear, a kit and a further kit. BACKGROUND It is understood that children’s feet grow rapidly, from infancy and toddlerhood, through early and middle childhood, to adolescence. During this rapid growth, a child will use many different sizes of shoe. The rapid growth of their feet means that a pair of shoes will commonly be outgrown before the pair of shoes is worn out or showing signs of excessive wear. Whilst it is possible to re-use or pass on pairs of shoes, as each shoe moulds to the user’s foot, this may not be ideal during growth of the foot. Furthermore, the majority of children’s shoes are thrown away, given the difficulty and cost in recycling the materials making up the shoe. An improved article of footwear is provided which addresses one or more problems associated with prior articles of footwear. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide an auxetic outsole for an article of footwear, an article of footwear and a kit as claimed in the appended claims. According to a first aspect of the invention, there is provided an auxetic outsole for an article of footwear, the outsole comprising an integrally formed sole unit having an upper surface, a lower surface and a periphery, the periphery including a lateral side and a medial side, and the sole unit comprising: a plurality of auxetic cavities provided in a region of the sole unit bounded by the periphery, wherein each auxetic cavity of the plurality of auxetic cavities extends through an entire thickness of the sole unit between the upper surface and the lower surface; and a plurality of periphery intersecting cavities, wherein at least one cavity of the periphery intersecting cavities intersects the periphery at the lateral side; and at least one cavity of the periphery intersecting cavities intersects the periphery at the medial side, each of the plurality of periphery intersecting cavities extends through an entire thickness of the sole unit between the upper surface and the lower surface. In certain embodiments, at least two of the periphery intersecting cavities intersect the periphery at the lateral side and / or at least of the periphery intersecting cavities intersect the periphery at the medial side. At least one auxetic cavity of the plurality of auxetic cavities is located between the at least two of the periphery intersecting cavities intersecting the periphery at the lateral side and between the at least two of the periphery intersecting cavities intersecting the periphery at the medial side. In certain embodiments, the region additionally includes one or more auxetic cavities in the heel region of the sole unit and / or one or more auxetic cavities in the toe region of the sole unit. The presence of the auxetic cavities and the periphery intersecting cavities enables the outsole to increase in length and width. In particular, the auxetic outsole may have a first condition and a second condition, wherein in the first condition the plurality of auxetic cavities and periphery intersecting cavities are narrow (i.e., non-stretched), and wherein in the second condition the plurality of auxetic cavities and periphery intersecting cavities are broad (i.e., stretched), such that the auxetic outsole is longer and wider in the second condition that in the first condition. A length of the outsole in the second condition may be at least between 5mm and 7mm longer than the length of the outsole in the first condition. The length of the outsole in the second condition may be at least 6mm longer than the length of the outsole in the first condition A size of the outsole in the second condition may be at least two Continental European sizes larger than that of the outsole in the first condition. The sole unit has an overall area, defined as the region of the top surface bound by the periphery, wherein the overall area of the sole unit in the second condition may be between 40% and 10% more than of the overall area of the sole unit in the first condition, preferably wherein the overall area of the sole unit in the second condition may be between 35% and 20% more than of the overall area of the sole unit in the first condition, preferably still wherein the overall area of the sole unit in the second condition may be 30% more than of the overall area of the sole unit in the first condition. In certain embodiments, one or more, or even all of the periphery intersecting cavities may be auxetic. The main function of the periphery intersecting cavities is to enable the periphery of the outsole to expand in a longitudinal direction and thereby not restrict expansion of the outsole in the longitudinal direction. The periphery intersecting cavities therefore do not need to be auxetic cavities but can be auxetic cavities. If the periphery intersecting cavities are auxetic cavities, in addition to allowing the outsole to expand in a longitudinal direction, they can also contribute to the expansion of the outsole in the width direction. In certain embodiments, the outsole can be cupped at the periphery. In other words, the periphery has an upwardly extending lip. Such a structure enables a force to be applied to the periphery of the outsole in order to place the outsole in the second (expanded) condition. The structure also provides a substrate to which the upper of the article of footwear can be attached, e.g., by stitching. As discussed in detail below, the plurality of auxetic cavities may be any suitable shape, provided they function as auxetic cavities, namely are able to expand in both length and width when a force is applied. In certain embodiments, the auxetic cavities have a curved shape in plan, i.e., when view from above. In certain embodiments, the plurality of auxetic cavities have a “figure of 8” shape in plan. The plurality of auxetic cavities can be arranged in any manner so as to enable the outsole to expand in both the longitudinal and width directions. In certain embodiments, the auxetic cavities form a repeating pattern across the outsole. In certain embodiments, the repeating pattern may extend from the centre of the outsole towards the periphery. In certain embodiments, the plurality of auxetic cavities may be oriented with a longitudinal axis of the outsole and a lateral axis of the outsole in an alternating fashion. In certain embodiments, the plurality of periphery intersecting cavities may be oriented so that pairs of the cavities are located on a lateral axis of the outsole, with one of the cavities intersects the periphery on the lateral side and the other cavity of the pair intersects the periphery on the medial side. In certain embodiments, one or more, or all of the plurality of auxetic cavities may have a chamfered edge at the upper surface and / or at the lower surface. According to a second aspect of the invention, there is provided an article of footwear comprising: an outsole according to the first aspect of the invention; a filler; and a stretchable upper. The stretchable upper may be joined to the outsole in any suitable manner, such as via a stitched connection or via an adhesive. In certain embodiments, the stretchable upper is joined to the outsole via stitching. The stitched connection may be continuous (i.e., the stitching connection joins the upper to the entire periphery of the outsole without any gaps), or may be intermittent (i.e., the stitching connection is not present at the location of one or more, or all, of the periphery intersecting cavities). In certain embodiments, the stitching is intermittent and not present at the location of all of the periphery intersecting cavities. The use of intermittent stitching ensures that expansion of the outsole at the periphery intersecting cavities is not restricted by the stitching connection. The stitched connection may be made using an elastic thread or an inelastic thread. Generally, when the stitching connection is continuous, an elastic thread is used so that expansion of the outsole at the periphery intersecting cavities is not restricted by the stitching connection. The stretchable upper may be any stretchable upper that stretches enough so as to be able to expand in size so as to accommodate the expansion of the outsole. Suitable stretchable uppers are well-known to those in the art and include knitted and woven uppers. The filler is a sole shaped unitary body. The filler is sized to fit in a complimentary way to the outsole. The filler is sufficiently rigid so as to apply sufficient outward pressure upon the periphery of the auxetic outsole so as to stretch the plurality of auxetic cavities and periphery intersecting cavities from their narrow form in the first condition to their broad form in the second condition, such that the auxetic outsole is longer and wider in the second condition that in the first condition. According to a third aspect of the invention, there is provided a kit comprising: an outsole according to the first aspect of the present invention; a plurality of fillers; and a stretchable upper, wherein the plurality of fillers comprise at least two fillers of different sizes. According to a fourth aspect of the invention, there is provided a kit comprising: an article of footwear according to the second aspect of the present invention; at least one or more additional fillers of different sizes. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of the auxetic outsole according to a first embodiment of the present invention; Figure 2 is a plan view of an outsole pattern; Figure 3 is a perspective view of the auxetic outsole of Figure 1, with two fillers of different sizes; Figure 4 is a perspective view of the outsole of Figure 1 combined with a filler and a knitted upper; Figure 5 is a perspective view of an auxetic outsole according to a second embodiment of the present invention; Figure 6 is a side elevation of the auxetic outsole of Figure 5;; Figure 7 is a perspective view of an auxetic outsole according to a third embodiment of the present invention; Figure 8 is a perspective view of an auxetic outsole according to a fourth embodiment of the present invention; and Figure 9 is an alternate perspective view of an auxetic outsole according to a fifth embodiment of the present invention. DETAILED DESCRIPTION Articles of footwear come in many forms, such as, but not limited to, shoes, trainers, boots, sandals, sneakers etc. An article of footwear commonly comprises an outsole, an upper and an insole. The outsole comprises the ground-contacting portion of the article of footwear. The upper retains the wearer’s foot and the insole provides cushioning or support for the sole of the user’s foot. Some articles of footwear do not include a separate insole, rather the wearer’s foot bears upon the upper surface of the outsole directly. Referring to Figure 1, an outsole 100 for an article of footwear is shown. The outsole shown in Figure 1 is for a user’s right foot. The outsole is an integrally formed sole unit, that is to say the sole unit is a unitary body. The outsole is integrally formed by various manufacturing techniques such as injection moulding. The sole unit has an upper surface 102, a lower surface 104 and a periphery 106. The periphery 106 bounds the integrally formed sole unit. The periphery 106 has a lateral side 110 and a medial side 112. The periphery has a toe end 111 and a heel end 113. A midfoot region 115 of the outsole is defined between the toe end 111 and heel end 113. The outsole has a longitudinal axis 140 which passes through the length of the outsole 100, from the toe end 111 to the heel end 113, between the lateral side 110 and the medial side 112. The outsole has a lateral axis 142, which passes through the width of the outsole 100, from the lateral side 110 to the medial side 112, between the toe end 111 and the heel end 113, i.e. in the midfoot region 115. The longitudinal axis 140 and lateral axis 142 intersect in the midfoot region 115. The sole unit has a plurality of auxetic cavities 120. Each auxetic cavity of the plurality of auxetic cavities 120 extends through an entire thickness of the outsole 100 between the up per surface 102 and the lower surface 104. The plurality of auxetic cavities 120 are provided in a region of the sole unit bounded by the periphery 106. Auxetic structures are those that are able to expand in both length and width when a force is applied to the structure. Auxetic structures can be characterized as having a negative Poisson’s ratio. Auxetic cavities are those that enable a material having such auxetic cavities to behave as an auxetic structure. As such the auxetic cavities enable the material to grow lengthwise and widthwise when a force is applied. The auxectic cavity can be any shape so long as they create the desired auxetic effect. Auxetic shapes are known to those skilled in the art. Various auxetic shapes may be used across the same outsole. Alternatively, similar or identical auxetic shapes may be used across the same outsole. The auxetic cavities are arranged so as to achieve the desired auxetic effect for the outsole 100. For example, the auxetic cavities can be arranged to have a specific orientation. The specific orientation can be altered to adjust how much width and length expansion is desired in the outsole 100. Referring to the specific example of Figure 1, the plurality of auxetic cavities 120 are provided in a first region 108 of the sole unit, where the first region 108 is within the periphery 106. The first region 108 covers the midfoot region 115 as well as a toe region (proximate the toe end 111) and a heel region (proximate the heel end 113). In certain embodiments, the outsole 100 is cupped, such that the periphery 106 is raised compared to the first region 108 of the sole unit, where a user’s foot would overlie in use. In other words, the periphery has an upwardly extending lip. The upper surface 102 of the sole unit may be substantially planar or may be contoured so as to provide support for the user’s foot in use, for example an arch support, etc. Each auxetic cavity of the plurality of auxetic cavities 120 has a similar form in plan view. The depth of each cavity can vary due to differences in the thickness of the outsole in the first region 108. Referring briefly to Figure 2, each cavity of the plurality of auxetic cavities 120 is an elongated figure “8” in plan view. An elongated figure “8” in plan view has a central axis 121 bisecting each circle forming the figure “8”. Each cavity is oriented to either be in line with the longitudinal axis 140 or lateral axis 142. That is, the central axis 121 of each auxetic cavity 120 is either parallel to or perpendicular to the longitudinal axis 140 of the outsole 100. The plurality of auxetic cavities 120 are distributed across the outsole 100 to alternate the orientation between those that are aligned with the longitudinal axis 140 and those that are aligned with the lateral axis 142. For example, starting at the heel end 113 and identifying each auxetic cavity between the heel end 113 and the toe end 111, a first auxetic cavity is aligned with the lateral axis 142, a second auxetic cavity is aligned with the longitudinal axis 140, A third auxetic cavity is aligned with the lateral axis 142, a fourth auxetic cavity is aligned with the longitudinal axis 140 and a fifth auxetic cavity is aligned with the lateral axis 142. A repeating pattern is thereby created across the outsole 100 (shown for example in Figure 2). The repeating pattern may be arranged to extend longitudinally and or laterally from a central point of the outsole 100, i.e. from the intersection of the longitudinal axis 140 and the lateral axis 142. This arrangement means that auxetic growth of the outsole 100 occurs in a manner that replicates the growth of the wearer’s foot. The repeating pattern may allow the plurality of auxetic cavities 120 to interlock across the first region 108. This may be exemplified by the interaction of the first auxetic cavity aligned with the lateral axis 142, and the second auxetic cavity aligned with the longitudinal axis 140, described above. Since both auxetic cavities have an elongated figure “8” in plan view, comprising a pair of circles connected at a waist, a circle forming part of the second auxetic cavity may be arranged adjacent to the waist of the first auxetic cavity to a closer extent than would be possible if the first auxetic cavity had an oblong form without a waist. Such an interlocking pattern allows a higher density of auxetic cavities 120 across the outsole 100. In an alternate embodiment, the auxetic cavity orientation can be modified further, such as at 30 or 45 degrees to the longitudinal and lateral axes in order to create a greater auxetic effect is other directions of the outsole 100. The auxetic cavities can be orientated in any manner in order to achieve the desired expansion of the outsole, e.g., the expansion of the outsole in both a longitudinal direction and a width direction. Furthermore, the orientation of the auxetic cavities can be altered to adjust how much width and length growth is desired in the outsole 100. The sole unit has a plurality of periphery intersecting cavities 130, wherein each cavity of the of the plurality of periphery intersecting cavities 130 extends through an entire thickness of the outsole 100 between the upper surface 102 and the lower surface 104. Each cavity of the plurality of periphery intersecting cavities 130 may be any shape so long as each cavity allows the periphery 106 to expand as part of the auxetic effect desired in the outsole 100. Each cavity of the plurality of periphery intersecting cavities 130 may be the same shape or different shapes according to their position on the outsole 100. Each or at least one of the cavities of the plurality of periphery intersecting cavities 130 may be part of the shape of the auxetic cavities used elsewhere on the outsole 100. The plurality of periphery intersecting cavities 130 are provided such that they each intersect a portion of the periphery 106. The plurality of periphery intersecting cavities 130 are arranged in a way that they create the desired auxetic effect for the outsole 100 in combination with the auxetic cavities. Referring to the specific example of Figure 1, each cavity of the plurality of periphery intersecting cavities 130 is arranged such that each cavity extends towards the longitudinal axis 140. The amount by which each cavity extends towards the longitudinal axis 140 depends upon the auxetic requirement of the outsole 100. Each cavity of the plurality of periphery intersecting cavities 130 extends towards the longitudinal axis 140 a sufficient distance to allow longitudinal extension of the outsole, especially the periphery of the outsole. As such each cavity of the plurality of periphery intersecting cavities 130 can extend towards the longitudinal axis 140 by any suitable amount such as 5mm to 50mm, or 5mm to 20mm. The plurality of periphery intersecting cavities 130 comprise: - a first cavity 132 rearward of the lateral axis 142 and extending through the periphery 106 on the lateral side 110; - a second cavity 134 forward of the lateral axis 142 and extending through the periphery 106 on the lateral side 110; - a third cavity 136 rearward of the lateral axis 142 and extending through the periphery 106 on the medial side 112; and - a fourth cavity 138 forward of the lateral axis 142 and extending through the periphery 106 on the medial side 112; Each cavity of the plurality of periphery intersecting cavities 130 extends toward the longitudinal axis 140 for approximately one third of the width of the outsole 100. Each cavity 132, 134, 136, 138 of the plurality of periphery intersecting cavities 130 has a similar shape in plan view; however, as will be appreciated by those skilled in the art, the plurality of periphery intersecting cavities can have different shapes. The cavities132, 134, 136, 138 are a partial elongated figure “8”. That is, as will be described below, the cavities are formed using the same tool shape. Because the cavities intersect the periphery, only a partial elongated figure “8” is formed. Each cavity 132, 134, 136, 138 is oriented to be in line with the lateral axis 142; however, as will be appreciated by those skilled in the art other orientations can be used. The cavities 132, 134, 136, 138 align with the repeating pattern created by the plurality of auxetic cavities 130. For example, the auxetic cavities overlying the intersection of the longitudinal axis 140 and the lateral axis 142 runs along the lateral axis 142, in parallel to, but offset from, each of the cavities 132, 134, 136, 138. Further auxetic cavities either-side of the lateral axis 142, run along the longitudinal axis 140 and sit between the cavities 132, 134, 136, 138, with a rearward auxetic cavity between the cavities 132 and 136 and the forward auxetic cavity between the cavities 134 and 138. The outsole 100 may be made using any suitable method, including moulding techniques. For example, the outsole 100 may be made using injection moulding. In the specific example of Figure 1, the outsole 100 is made using injection moulding using a silicone rubber mould. This moulding method facilitates extraction of the outsole 100 from the mould without damaging the outsole 100 in the region of the plurality of auxetic cavities 120 and the plurality of cavities 130. Conditions Referring to Figure 3, the outsole 100 is shown together with two fillers of different sizes. For the purposes of explanation, a small filler 170 and a large filler 180 are shown. The small filler 170 is a sole shaped unitary body. The small filler 170 has a lateral side 172 and a medial side 174. The small filler 170 has a toe end 176 and a heel end 178. The small filler 170 is largely flat, however it may have some curvature, for example towards the toe end 176. The small filler 170 may have an undulating upper surface, for example to provide arch support to the wearer. The small filler 170 is rigid, in particular towards the toe end 176 and the heel end 178. The large filler 180 is a sole shaped unitary body. The large filler 180 has a lateral side 182 and a medial side 184. The large filler 180 has a toe end 186 and a heel end 188. The large filler 180 is largely flat, however it may have some curvature, for example towards the toe end 186. The large filler 180 may have an undulating upper surface, for example to provide arch support to the wearer. The large filler 180 is rigid, in particular towards the toe end 186 and the heel end 188. The large filler 180 is larger in length and width than the small filler 170. The small and large fillers 170, 180 may be made of a similar material. The small and large fillers 170, 180 may be made of a thermoplastic polyurethane (TPU). Referring to Figure 4, the outsole 100 is connected to a stretchable upper 190. The stretchable upper 190 may be any suitable stretchable upper, including knitted and woven uppers. The stretchable upper 190 sits within the cupped periphery 106 of the outsole 100. The outsole 100 is connected to the stretchable upper 190 by a stitch 194. An elastic thread is used for the stitch 194. The stitch 194 is intermittent, in that there is no stich across the periphery intersecting cavities 130. The cupped periphery 106 of the outsole 100 facilitates stitching of the stretchable upper 190 to the outsole 100. The stich 194 allows simple dismantling of the article of footwear, improving the ease of recycling, such that the stretchable upper 190, outsole 100 and fillers 170, 180 may be easily disassembled, without complicated steps relating to the removal of an adhesive. The small and large fillers 170, 180 are alternately placed inside the stretchable upper 190 and bear upon the cupped periphery 106, through the stretchable upper 190, to apply an outward force to the cupped periphery 106. The small and large fillers 170, 180 are shaped to engage with the periphery 106. In particular, the rigid toe and heel ends 176, 186, 178, 188 of the small and large fillers 170, 180 bear upon the cupped periphery 106. In use, downward pressure from the user’s foot helps retain the small or large fillers 170, 180 in place. The periphery 106 may be provided with a groove at the toe end 111. The periphery 106 may be provided with a groove at the heel end 113. The small and large fillers 170, 180 may be provided with complimentary features to engage with one of or both of the grooves provided at the toe end 111 and heel end 113. The periphery 106 and the toe and heel ends 176, 186, 178, 188 of the small and large fillers 170, 180 may be provided with interlocking features. In a first condition, using the small filler 170, the plurality of auxetic cavities 120 are narrow. In a second condition, using the large filler 180, the plurality of auxetic cavities 120 are broad. This is because the large filler 180 applies a greater outward force upon the cupped periphery 106. The overall length of the auxetic outsole 100 (from the toe end 111 to the heel end 113) is longer in the second condition than in the first condition. Likewise, the overall width of the auxetic outsole 100 (from the lateral side 110 to the medial side 112) is wider in the second condition than in the first condition. Similarly, in the first condition the plurality of periphery intersecting cavities 130 are narrow. In the second condition the plurality of periphery intersecting cavities 130 are broad. The overall length of the auxetic outsole 100 (from the toe end 111 to the heel end 113) is longer in the second condition that in the first condition. In an exemplary embodiment, the length of the outsole 100 (from the toe end 111 to the heel end 113) in the second condition is at least between 5mm and 7mm longer than the length of the outsole 100 in the first condition. In an exemplary embodiment the length of the outsole 100 (from the toe end 111 to the heel end 113) in the second condition is at least 6mm longer than the length of the outsole 100 in the first condition. Articles of footwear, such as shoes, are sized according to different measures and systems. One such measure is the Continental European system, whereby the shoe size is derived from the length of a last. The different measures and systems can be compared using conversion charts. An exemplary conversion chart is shown in Table 1 below. Footlength (mm) UK size EU size USA size 115 3 19 4 119 3.5 19.5 4.5 123 4 20.5 5 126 4.5 21 5.5 130 5 21.5 6 134 5.5 22 65 138 6 23 7 142 6.5 23.5 7.5 146 7 24 8 149 7.5 25 8.5 153 8 25.5 9 157 8.5 26 9.5 161 9 26.5 10 165 9.5 27.5 10.5 169 10 28 11 172 10.5 28.5 11.5 176 11 29 12 180 11.5 30 12.5 184 12 30.5 13 188 12.5 31 13.5 192 13 32 1 196 13.5 32.5 1.5 200 1 33 2 204 1.5 33.5 2.5 209 2 34.5 3 213 2.5 35 3.5 217 3 35.5 4 221 3.5 36 4.5 226 4 37 5 230 4.5 37.5 5.5 234 5 38 6 238 5.5 38.5 6.5 242 6 39 7 246 6.5 40 7.5 251 7 41 8 255 7.5 41.5 8.5 259 8 42 9 Table 1 In Table 1, the first column shows the approximate foot length in millimetres (mm), the second column shows the equivalent United Kingdon (UK) size, the third column shows the equivalent Continental European (EU) size and the fourth column shows the equivalent United States of America (USA) size. The growth in the size of the outsole 100 can be a change of between 1, 2 or 3 Continental European sizes between the first condition and the second condition. In some embodiments, the overall size of the outsole 100 in the second condition is two Continental European sizes larger than that of the size of the outsole in the first condition. In some embodiments, the overall size of the outsole 100 increase in both the length and width in the second condition compared to the first condition. In some embodiments, the plurality of periphery intersecting cavities 130 are not limited to the lateral side 110 and the medial side 112 of the periphery 106. One or more periphery intersecting cavities 130 may also be provided at the periphery 106 at the toe end 111 and / or the heel end 113. Such toe end or heel end periphery intersecting cavities 130 function to enable the periphery of the outsole to expand in a lateral direction and thereby not restrict expansion of the outsole in the lateral direction. Such toe end or heel end periphery intersecting cavities 130 therefore do not need to be auxetic cavities but can be auxetic cavities. If the toe end or heel end periphery intersecting cavities 130 are auxetic cavities, in addition to allowing the outsole to expand in a lateral direction, they can also contribute to the expansion of the outsole in the length direction. In some embodiments, the increase in length and width of the outsole 100 between the second condition and the first condition results in an increase in overall area of the outsole 100 of between 40% and 10%, or between 35% and 20% or approximately 30%. Referring to Figures 5 and 6, an outsole 200 for an article of footwear in accordance with another embodiment of the present invention is shown. Similar reference numbers are used to reference similar features of the outsole 200 as compared to the outsole 100, prefixed with a “2” rather than a “1” to indicate that they relate to the outsole 200. Only substantial differences shall be described in detail. The outsole is for a user’s right foot. The outsole is an integrally formed sole unit having an upper surface 202, a lower surface 204 and a periphery 206. The periphery 206 bounds the integrally formed sole unit. The periphery 206 has a lateral side 210 and a medial side 212. The periphery has a toe end 211 and a heel end 213. A midfoot region 215 of the outsole is defined between the toe end 211 and heel end 213. The outsole has a longitudinal axis 240 which passes through the length of the outsole 200, from the toe end 211 to the heel end 213, between the lateral side 210 and the medial side 212. The outsole has a lateral axis 242, which passes through the width of the outsole 200, from the lateral side 210 to the medial side 212, between the toe end 211 and the heel end 213. The longitudinal axis 240 and lateral axis 242 intersect in the midfoot region 215. The sole unit has a plurality of auxetic cavities 220. Each auxetic cavity of the plurality of auxetic cavities 220 extends through an entire thickness of the outsole 200 between the upper surface 202 and the lower surface 204. The plurality of auxetic cavities 220 are provided in a first region 208 of the outsole 200, where the first region 208 is within the periphery 206. The first region 208 covers the midfoot region 215 as well as a toe region (proximate the toe end 211) and a heel region (proximate the heel end 213). The outsole 200 is cupped, such that the periphery 206 is raised compared to the first region 208 of the outsole, where a user’s foot would overlie in use. Furthermore, the outsole 200 has a complex curvature on the upper surface 202. The complex curvature supports the user’s foot in use. Given the complex curvature of the upper surface 202, the depth of each cavity varies according to the thickness of the outsole in the first region 208. The plurality of auxetic cavities 220 comprises four individual auxetic cavities. The four individual auxetic cavities are oriented to be in line with the lateral axis 242. The four individual auxetic cavities are arranged from the toe end 211 to the heel end 213, as follows: A first auxetic cavity 222; A second auxetic cavity 224; A third auxetic cavity 226; and A fourth auxetic cavity 228. The first, second and third auxetic cavities 222, 224, 226 of the plurality of auxetic cavities 220 are each an elongated upper-character “I” in plan view. Thus the shape of each of the first, second and third auxetic cavities 222, 224, 226 is that of a central channel with two side channels at each end of the central channel, wherein at each end the two side channels extend away from the central channel in opposite substantially perpendicular directions. The fourth auxetic cavity 228 of the plurality of auxetic cavities 220 is an elongated uppercharacter “C” in plan view. Thus the shape of the fourth auxetic cavity 228 is of a central channel with a side channel at each end of the central channel, wherein the side channels extend away from the central channel at approximately 45 degrees from the lateral axis, towards the toe end 211. The first auxetic cavity extends across the midfoot region 215 adjacent the toe end 211 in parallel to the lateral axis 242. The second auxetic cavity extends across the midfoot region 215 approximately equidistant from the toe end 211 and the heel end 213, and in parallel to the lateral axis 242. The third auxetic cavity 226 extends across the midfoot region 215 in parallel to the lateral axis 242. The fourth auxetic cavity 228 extends across the midfoot region 215 adjacent the heel end 213 in parallel to the lateral axis 242. Thus each of the central channels referred to above run in parallel to the lateral axis 242. The sole unit has a plurality of periphery intersecting cavities 230, wherein each cavity of the of the plurality of periphery intersecting cavities 230 extends through an entire thickness of the outsole 200 between the upper surface 202 and the lower surface 204. The plurality of periphery intersecting cavities 230 are provided in: a second region 214 of the outsole 200 which intersects the lateral side 210 of the periphery 206; and a third region 216 of the outsole 200 which intersects a medial side 212 of the periphery 206. The plurality of cavities 230 therefore comprise: - a first cavity 232 rearward of the lateral axis 242 and extending through the periphery 206 on the lateral side 210; - a second cavity 234 forward of the lateral axis 242 and extending through the periphery 206 on the lateral side 210; - a third cavity 235 further forward of the lateral axis 242 and extending through the periphery 206 on the lateral side 210; - a fourth cavity 236 rearward of the lateral axis 242 and extending through the periphery 206 on the medial side 212 - a fifth cavity 238 forward of the lateral axis 242 and extending through the periphery 206 on the medial side 212; and - a sixth cavity 239 further forward of the lateral axis 242 and extending through the periphery 206 on the medial side 212. The term forward is used to define a relative position on the sole unit towards the toe end 211. The term rearward is used to define a relative position on the sole unit towards the heel end 213. Each cavity of the plurality of periphery intersecting cavities 230 extend toward the longitudinal axis 240 for approximately one third of the width of the outsole 200. Each cavity 232, 234, 235, 236, 238, 239 of the plurality of periphery intersecting cavities 230 has a similar shape in plan view. Each cavity 232, 234, 235, 236, 238, 239 is a partial elongated upper-character “I” in plan view. Thus the shape of each cavity 232, 234, 235, 236, 238, 239 of the plurality of periphery intersecting cavities 230 is that of a central channel with two side channels at the end of the central channel, wherein the two side channels extend away from the central channel in opposite substantially perpendicular directions. Each cavity 232, 234, 235, 236, 238, 239 is oriented to be in line with the lateral axis 242. Therefore each central channel is parallel to the lateral axis 242. As can be seen in Figure 6, where the central channel intersects the periphery 206, the width W of the central channel is the same for each of the periphery intersecting cavities 230. The first and fourth cavity 232, 236 are aligned with respect to their longitudinal position between the toe end 211 and the heel end 213. The central channels of the first and fourth cavity 232, 236 may be described as a pair. The first and fourth cavity 232, 236 are closer to the heel end 213 than to the toe end 211. The second and fifth cavity 234, 238 are aligned with respect to their longitudinal position between the toe end 211 and the heel end 213. The central channels of the second and fifth cavity 234, 238 may be described as a pair. The second and fifth cavity 234, 238 are approximately equidistant between the toe end 211 and the heel end 213. The third and sixth cavity 235, 239 are aligned with respect to their longitudinal position between the toe end 211 and the heel end 213. The central channels of third and sixth cavity 235, 239 may be described as a pair. The third and sixth cavity 235, 239 are closer to the toe end 211 than to the heel end 213. The plurality of auxetic cavities 220 align with, but are offset from the plurality of periphery intersecting cavities 230. This means that moving along the longitudinal axis 240 between the toe end 211 to the heel end 213 the central channels of the auxetic cavities 220 and the periphery intersecting cavities 230 are encountered in an alternating fashion, with each central channel of the auxetic cavities 200 occupying a different longitudinal position relative to each pair of central channels of the periphery intersecting cavities 230. The outsole 200 functions in the same way as outsole 100, which shall not be described in detail here. Referring to Figure 7, an outsole 300 for an article of footwear in accordance with another embodiment of the present invention is shown. Similar reference numbers are used to reference similar features of the outsole 300 as compared to the outsole 100, prefixed with a “3” rather than a “1” to indicate that they relate to the outsole 400. Only substantial differences shall be described in detail. The fourth auxetic cavity 328 has the same shape as each of the first, second and third auxetic cavities 322, 324, 326. An additional fifth auxetic cavity 329 is provided in the outsole 300. The fifth auxetic cavity 329 extends across the midfoot region 315 adjacent the toe end 311 in parallel to the lateral axis 342. The shape of the fifth auxetic cavity 329 is of a central channel with a side channel at each end of the central channel, wherein the side channels extend away from the central channel at approximately 45 degrees from the lateral axis, towards the heel end 311. Compared to the outsole 200, the outsole 300 has an additional pair of periphery intersecting cavities 352, 354 towards the toe end 311 of the outsole 300, between the fourth and fifth auxetic cavities 328, 329. The outsole has another additional pair of periphery intersecting cavities 356, 358 towards the heel end 313 of the outsole 300. Referring to Figure 8 , an outsole 400 for an article of footwear in accordance with another embodiment of the present invention is shown. Similar reference numbers are used to reference similar features of the outsole 400 as compared to the outsole 200, prefixed with a “4” rather than a “2” to indicate that they relate to the outsole 400. Only substantial differences shall be described in detail. Each auxetic cavity of the plurality of auxetic cavities 420 has a chamfered edge 421 on the upper surface 402. The chamfered edge supports the changes in size of the outsole 400, reducing localised stress concentrations forming in the outsole 400 at the auxetic cavities 420. In another embodiment each auxetic cavity of the plurality of auxetic cavities 420 has a chamfered edge on the lower surface 404. In another embodiment each cavity of the plurality of periphery intersecting cavities 430 has a chamfered edge on the upper surface 402. In another embodiment each cavity of the plurality of periphery intersecting cavities 430 has a chamfered edge on the lower surface 404. Referring to Figure 9, an outsole 500 for an article of footwear in accordance with another embodiment of the present invention is shown. Similar reference numbers are used to reference similar features of the outsole 500 as compared to the outsole 200, prefixed with a “5” rather than a “2” to indicate that they relate to the outsole 500. Only substantial differences shall be described in detail. The lower surface 504 is provided with a series of pads 598 positions between the plurality of auxetic cavities 520 and the plurality of periphery intersecting cavities 530. The series of pads 598 reduce the volume of material required to produce the outsole 500, whilst retaining the same cushioning and supportive effect of the outsole 500. By reducing the volume of material required to produce the outsole 500, the same auxetic effect can be achieved with smaller or fewer auxetic cavities. Equally, by reducing the volume of material required to produce the outsole 500 a larger auxetic effect can be achieved with the same number and or size of auxetic cavities.

Claims

1. An auxetic outsole for an article of footwear, the outsole comprising:an integrally formed sole unit having an upper surface, a lower surface and a periphery, the periphery including a lateral side and a medial side, andthe sole unit comprising:a plurality of auxetic cavities provided in a region of the sole unit bounded by the periphery, wherein each auxetic cavity of the plurality of auxetic cavities extends through an entire thickness of the sole unit between the upper surface and the lower surface; and a plurality of periphery intersecting cavities, wherein at least one cavity of the periphery intersecting cavities intersects the periphery at the lateral side; and at least one cavity of the periphery intersecting cavities intersects the periphery at the medial side, each of the plurality of periphery intersecting cavities extends through an entire thickness of the sole unit between the upper surface and the lower surface.

2. The auxetic outsole according to claim 1 wherein at least two of the periphery intersecting cavities intersect the periphery at the lateral side.

3. The auxetic outsole according to claim 1 or claim 2 wherein at least two of the periphery intersecting cavities intersect the periphery at the medial side.

4. The auxetic outsole according to claim 3 wherein at least one auxetic cavity of the plurality of auxetic cavities is located between the at least two of the periphery intersecting cavities intersecting the periphery at the lateral side and between the at least two of the periphery intersecting cavities intersecting the periphery at the medial side.

5. The auxetic outsole according to claim 4 wherein the region additionally includes one or more auxetic cavities a heel region of the sole unit.

6. The auxetic outsole according to claim 4 or claim 5 wherein first region additionally includes one or more auxetic cavities in a toe region of the sole unit.

7. The auxetic outsole according to claim 1, wherein the auxetic outsole has a first condition and a second condition, wherein in the first condition the plurality of auxetic cavities and the periphery intersecting cavities are narrow, and wherein in the second condition the pluralityof auxetic cavities and periphery intersecting cavities are broad, such that the auxetic outsole is longer and wider in the second condition that in the first condition.

8. The auxetic outsole according to claim 7, wherein a length of the outsole in the second condition is at least between 5mm and 7mm longer than the length of the outsole in the first condition, preferably where the length of the outsole in the second condition is at least 6mm longer than the length of the outsole in the first condition.

9. The auxetic outsole according to claim 7, wherein a size of the outsole in the second condition is at least two Continental European sizes larger than that of the outsole in the first condition.

10. The auxetic outsole according to any of claims 7 to 9, wherein the sole unit has an overall area, defined as the region of the top surface bound by the periphery, wherein the overall area of the sole unit in the second condition is between 40% and 10% more than of the overall area of the sole unit in the first condition, preferably wherein the overall area of the sole unit in the second condition is between 35% and 20% more than of the overall area of the sole unit in the first condition, preferably still wherein the overall area of the sole unit in the second condition is 30% more than of the overall area of the sole unit in the first condition.

11. The auxetic outsole according to any preceding claim, wherein one or more of the periphery intersecting cavities are auxetic, preferably wherein all of the periphery intersecting cavities are auxetic.

12. The auxetic outsole according to any preceding claim, wherein the outsole is cupped at the periphery.

13. The auxetic outsole according to any preceding claim, wherein the plurality of auxetic cavities have a curved shape in plan.

14. The auxetic outsole according to any preceding claim, wherein the plurality of auxetic cavities have a “figure of 8” shape in plan.

15. The auxetic outsole according to any preceding claim, wherein the plurality of auxetic cavities form a repeating pattern across the outsole, preferably wherein the repeating pattern extends from the centre of the outsole towards the periphery.

16. The auxetic outsole according to any preceding claim, wherein the plurality of auxetic cavities are oriented with a longitudinal axis of the outsole and a lateral axis of the outsole in an alternating fashion.

17. The auxetic outsole according to any preceding claim, wherein the plurality of periphery intersecting cavities are oriented so that pairs of the cavities are located on a lateral axis of the outsole, with one of the cavities intersects the periphery on the lateral side and the other cavity of the pair intersects the periphery on the medial side.

18. The auxetic outsole according to any preceding claim, wherein one or more or all of the plurality of auxetic cavities have a chamfered edge at the upper surface and / or at the lower surface.

19. An article of footwear comprising:an outsole according to claim 1;a filler; anda stretchable upper.

20. An article of footwear according to claim 19, wherein the stretchable upper is joined to the outsole via a stitched connection.

21. An article of footwear according to claim 20, wherein the stitched connection is intermittent and not present at the location of all of the periphery intersecting cavities.

22. An article of footwear according to claim 20, wherein the stitched connection includes an elastic thread.

23. An article of footwear according to claim 19, wherein the stretchable upper is knitted, woven or sewn.

24. A kit comprising:an outsole according to claim 1;a plurality of fillers; anda stretchable upper, wherein the plurality of fillers comprise at least two fillers of different sizes.

25. A kit comprising:an article of footwear according to claim 19;at least one or more additional fillers of different sizes.

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