Technical field

The present invention is relative to a multi-layered sole for heeled footwear, in particular having a system providing cushioning and support for the comfort of the wearer.

Technological background

The use of high-heeled shoes, which are considered to be shoes having a heel above 40 mm, is prevalent in today's women fashion and their use is widespread . Typically, high heeled shoes are so designed that the heel of the foot which is wearing such a shoe is placed in a higher position - in particular much higher - than the toes and the foot is substantially lying on an inclined plane. This particular configuration has the reputation by many women to be extremely uncomfortable, due to the fact that the forces which the foot is subjected to are acting on portion(s) of the foot which are not the same as in standard "flat" shoes.

Therefore, in the technical field of shoes' design and construction, the need of comfortable high-heeled shoes, which provide for support and stability to prevent injuries to the wearer, and for flexibility in order to allow the foot of the wearer to bend while walking, is extremely felt since long time. In order to find a solution to this need, however, also limitations on the design of the shoes itself have to be taken into account, due to the fact that the size and shape of women shoes has to satisfy a plurality of requirements which are dictated by fashion . One of these limitations is, for example, the overall thickness of the sole, which has to be as thin as possible, to give a "light" appearance to the shoes. In other words, the comfort, given for example by cushioning means or shock absorption means attached to the sole, has to go hand in hand with style and appearance, in order to be accepted and bought by the consumers.

Several attempts have been made in order to solve the aforementioned problems and satisfy the need of comfortable stylish high-heeled shoes. Patent application US 2009/0188131 discloses a shoe construction including a shoe upper, an intermediate composite structure and an outsole. The composite structure underlies at least a portion of the upper and overlies at least a portion of the outsole. The composite structure includes cushion members with one cushion member being positioned to underlie a heel of a wearer and another cushion member being positioned to underlie the ball of the foot. The cushion member underlying the ball may be perforated. The composite structure can also include a relatively rigid lower member which can be perforated in the area of the ball of the foot underlying the cushion member for the ball of the foot. The composite structure can provide a flexure discontinuity in the shoe forward of the midfoot zone of the shoe. Patent application US 2007/011918 shows a shoe with increased flexibility in a forefoot portion that includes an upper, an upper lining, an outsole, a footbed and a flexible insole. The flexible insole is located in the forefoot portion of the upper and is stitched directly to the upper lining along a perimeter of the flexible insole. The footbed includes a heel pad that is located in the heel portion of the shoe.

Patent application US 2009/0255148 is relative to a device for insertion in a high-heeled shoe has a first crescent shaped raised area in a region underlying the forward edge of a wearer's heel bone and a second raised area underlying the metatarsals of the wearer is described . Also described is a method for constructing a shoe using the device and the resulting shoe. Patent application US 2007/124960 describes a shoe comprising a foot retaining portion having a heel area and having an interior side, the interior side sized and shaped to hold a foot and including an upper portion, the upper portion optionally lined with a pliable material; a first exterior insole layer having therein a cut-out adjacent the heel area of the foot retaining portion, the first exterior inside layer having an interior surface forming the bottom of the foot retaining portion and that is lined with pliable material; a second exterior insole layer having a heel strike pad sized and shaped to fit within the cut-out of the first exterior insole layer, the heel strike pad comprised of a material that absorbs and disperses heel strike forces; a third exterior insole layer sized to fit the foot retaining portion and having therein a cut-out adjacent the heel area of the foot retaining portion, the third exterior insole layer comprised of a material that provides foot cushioning; a fourth exterior insole layer adjacent the third exterior insole layer comprised of a material that provides foot tactile stimulation when foot pressure is applied thereto; an outsole layer adjacent the fourth exterior insole layer comprised of a material that provides outsole flexibility and skid resistance, the outsole layer having a heel with an optional depression therein; and an optional heel strike pad sized and shaped to fit within the depression of the heel of the outsole layer and comprised of a material that absorbs and disperses heel strike forces.

Patent application US 2004/0250448 discloses a footwear cushioning system including an insole and a midsole that define a chamber containing multiple, hollow, inverted, truncated cones. The insole includes a plate having a downwardly extending rib to define a recess. The midsole includes a midsole plate including an upwardly extending wall and multiple upwardly opening hollow, inverted frusto-conical cushion cells. The wall interfits within the rib, and the cushion cells abut against the insole plate. An outsole shell is direct-attached to the cushioning system with polyurethane. Preferably, the polyurethane pre- com presses the cushion cells and adds cushioning and energy return characteristics. To assemble the cushion system, an upper is stapled to the insole rib. The midsole is interfitted within the rib. The insole and midsole are heated to fuse the cushion cells to the insole. Polyurethane is poured into the outsole shell and the shell is direct attached to the upper/cushioning system.

Patent US 5699627 describes components for the manufacture of a shoe include a shoemaker's last, a padded sole member, an insole assembly, an antiskid damping sole and a heel assembly. These components may be used together or combinations thereof may be used in the manufacture of shoes for women, men or children.

Patent US 5619809 shows a footwear sole assembly for providing air circulation around the foot and also providing improved resilient cushioning . The assembly includes an outsole and an insert suspended above the outsole in trampoline-like fashion to define an air chamber therebetween. As the wearer strides, the insert moves toward the outsole compressing the air contained in the air chamber and causing that air to flow onto the foot through the apertures in the insert. Preferably, the outsole defines a plurality of upwardly opening pockets; and the insert includes a plurality of downwardly extending pins aligned with the pockets. The flexing action of the insert also drives the pins down into the pockets where they are deformed to absorb the impact of the stride.

Summary of the invention

The present invention relates to a multi-layered sole for heeled footwear which allows obtaining footwear having high stability and comfort for the wearer keeping at the same time the thickness of the multi-layered structure comparable with the thickness of standard sole for heel shoes, therefore safeguarding the stylish fashionable appearance.

In the following, with the term "heeled footwear", footwear having a heel of a height of about 40 mm and above is meant. In some cases, due to the presence of platforms or similar accessories, the heel height is not the determinant factor, "heeled footwear" in this case means a footwear in which the difference between the level of the position of the toes and the level of the heel of the wearer is of at least about 40 mm. The actual shape of the heel is of no relevance for the application of the invention and it can be of any type, ranging from stilettos to spool heel, kitten heel, wedge heel, block heel, etc.

In addition, the sole of the invention is intended for use in a wide variety of footwear, e.g . it can be incorporated into shoes, boots, sandals, platforms, pumps and other soled footwear.

Generally, heeled footwear is used by women; however the present invention is applicable in a variety of men footwear as well according to the applicable rules of fashion. The foot of a person can be considered to include three regions substantially parallel one to the other and dividing the foot in three portions along its longitudinal extension. The forefoot region is the region "in the front", i.e. the region of the toes (called phalanges) and the metatarsal region; the midfoot region is the region "in the middle", it includes five irregularly shaped tarsal bones, forms the foot's arch, and serves as a shock absorber. The hindfoot region is the back part of the foot and it is composed of three joints linking the midfoot to the ankle (talus). The top of the talus is connected to the two long bones of the lower leg (tibia and fibula), forming a hinge that allows the foot to move up and down. The heel bone (calcaneus) is the largest bone in the foot. The bones of the midfoot are connected to the forefoot and the hindfoot by muscles and the plantar fascia (arch ligament). The ball of the foot is where the toes join with the rest of the foot, i.e. the portion of the foot sole between the toes and the arch.

In a sole for footwear, the same three regions, i.e. forefoot, midfoot and hindfoot region, can be recognized as being the regions corresponding to the homonymous part of the foot, i.e. the forefoot region of the sole is the part of the sole on which the forefoot region of the foot lies on or above when the footwear is worn by the wearer, etc.. Applying the same analogy, also a ball region can be identified in the sole, which is one of the regions of the sole, together with the heel region, on which most of the wearer weight is applied when she/he is wearing high heeled shoes. Indeed, the ball is the region of the foot where the weight of the body rests when the heel is raised . Therefore, the sole can be analogously considered as divided in three parallel regions along the longitudinal direction. Also all the other regions defined in the foot, i.e. the arch region, the metatarsal region, the heel region, etc, find their corresponding counterpart on the sole applying the same aforementioned analogy

Additionally, reference to "lateral side" means the outside of the foot, while reference to "medial side" means the side of the foot where the arch is located . As mentioned above, the same terminology can be applied to the different parts of a sole, which comprises then two sides in a manner substantially perpendicular to the forefoot, midfoot and hindfoot regions above defined .

The multi-layered sole of the invention includes two elements, a first layer, which can be also considered as an insole or footbed, and a second layer, which can be also considered as a midsole.

These two layers are preferably sandwiched between an outsole, which is the layer in direct contact with the ground, and a liner, which is the layer in direct contact with the wearer foot.

The outsole can be realized in any material, such as leather or resin rubber, natural rubber or a synthetic material like polyurethane. The outsole may comprise a single piece, or may be an assembly of separate pieces of different materials. The outsole in correspondence of the heel portion includes the heel . The thickness of the outsole, not considering the heel, preferably is comprised between 3.5 mm and 10 mm. The height of the heel is preferably comprised between 40 mm and 110 mm.

The liner can be also realized in any standard material such as fabric, leather or rubber. In addition, preferably it has undergone antibacterial treatment(s), according to the known art. Preferably, the liner comprises a plurality of through-holes which permits air communication between the area where the foot is located and the first layer, as better clarified below. Preferably, the thickness of the liner is comprised between 0.6 mm and 1.2 mm.

The second layer is the layer that gives stability to the footwear. It preferably includes a shank, more preferably made of steel, to give stability to the overall sole and avoid breakage of the same. The shank is preferably embedded in the second layer and does not surface. Moreover, the second layer defines two surfaces, the first one which is connected to the outsole and which is substantially smooth, and the second one which includes a peripheral wall which follows the edge of the layer for the whole hindfoot region and for at least a portion of the midfoot region. More preferably, the peripheral wall extends from the tip of the hindfoot region for about 60% of the length of the sole symmetrically with respect to the longitudinal axis of the sole on the lateral and medial sides. Therefore, the longitudinal extension of the peripheral wall depends on the length of the sole. The thickness of the wall is substantially preferably uniform and it is comprised between 5 mm and 6 mm.

The portion of the second surface corresponding to the forefoot region on the contrary is smooth without protruding elements. The peripheral wall defines a seat in which a corresponding portion of the first layer is received, as better detailed in the following, and it gives support to the talus and stability to the overall sole when the wearer is walking.

The thickness of the second layer may vary depending on the considered region of the same. In the flat portion corresponding to the forefoot region, the thickness of the second layer is substantially uniform and preferably comprised between 0.8 mm and 1.2 mm. From the end of the forefoot region or from the beginning of the midfoot region, the thickness of the second layer gradually increases up to a thickness of between 9 mm and 12 mm at the heel region.

The second layer comprises in the midfoot and partially in the hindfoot region a longitudinal step having a height preferably comprised between 1,5 mm and 2,5 mm in thickness, preferably having a width comprised between 20 mm and 30 mm and preferably a length comprised between 120 mm and 130 mm for housing the shank.

The material in which the second layer is realized can be any suitable material, preferably a polymer like polyoxymethylene (POM), polyacrylonitrile (PAN), acrylonitrile butadiene styrene (ABS), polyvinyl chloride (PVC), polyether ether ketone (PEEK), polyurethane (PU), polyethylene terephthalate (PET), polyethylene (PE), polystyrene (PS) or polypropylene (PP), or a composite material like fiberglass, carbon fiber or Kevlar™. Preferably the material is re-cycled .

The first layer allows an optimal distribution of the load weight in the footwear, in particular for footwear having a heel higher than 50 mm. The combination of a first and a second layer gives a synergy effect combining the possibility of free comfortable movements and retention given by the cushioning elements below described, keeping however the overall thickness of the sole limited.

The first layer includes a first and a second surface, the first surface being substantially smooth and fixed to the liner, while the second surface is in contact with the second layer, more in particular the first layer is partially inserted in the seat formed by the peripheral wall in the hindfoot region and at least partially in the midfoot region.

The first layer includes a specific padding/cushioning structure which will be described in detail . This structure, in correspondence of the forefoot region and partially in the midfoot region, and more particularly in correspondence of the ball region, includes a pad, which is substantially a shock absorber insert located in the area where the metatarsal load is higher, due to the inclined position of the foot of the wearer wearing high heels. The pad reduces the pressure on the forefoot and thus decreases the risk of joint irritations at the same time increasing the comfort of the footwear. The pad can be either fixed to the first or second surface of the first layer, for example by gluing, or molded together with the first layer forming an integral piece. Preferably, the material in which the pad is realized is softer than the material in which the first layer is realized . Alternatively, pad and first layer can be realized in the same material but with different densities. The pad gives also a "spring effect", i.e. the material in which it is realized has a shape memory, thus when it is deformed by the pressure of the foot which bends in the walking activity, it tends to go back to the original shape "pulling" the forefoot of the wearer. Further, the pad can be of any suitable form. Preferably, the pad has a maximum thickness comprised between 7 mm and 10 mm.

The preferred materials in which the first layer and/or the pad and/or the cushioning element below described are formed are polyurethane (PU), ethylene vinyl acetate (EVA), phylon , phylite , solyte , thermoplastic materials.

Additionally, the padding/cushioning structure, in correspondence of a portion of the hindfoot region and of the midfoot region of the first layer, includes a cushioning element which has been designed by Applicants after a study of the postural and physiological load distribution in the cycle gait of humans. Preferably, the cushioning element projects from the second surface of the first layer. The aim of the construction of the cushioning element is to give the highest comfort to the wearer of the footwear. Studying the gait cycle, it has been seen by Applicants that there is a physiological torsion of the foot and a change in the load distribution while walking . The natural movement therefore has been facilitated developing a cushioning element which has a higher thickness in correspondence of the plantar arch and part of the metatarsal region.

According to the above study, the thickness of the cushioning element varies at least from a first higher thickness in correspondence of the medial region of the midfoot region, i.e. of the region towards the inner part of the first layer in the midfoot region which corresponds substantially to the arch region; and a second smaller thickness in the other region(s). More preferably, the cushioning element has a plurality of thicknesses, for example the thickness smoothly decreases from the midfoot region to the forefoot region where it becomes substantially equal to zero to continuously connect the forefoot region where no cushioning is present. In addition, the thickness of the cushioning element is rather low in correspondence of the heel region, even more preferably in the heel region the thickness of the cushioning element is at its minimum.

This cushioning element is partially inserted in the seat defined in the second layer by the peripheral wall.

According to a preferred embodiment of the invention, the cushioning element is realized by a plurality of protuberances - or pins - having of different heights. The protuberances are substantially cylinders or truncated cones having an arbitrary cross section projecting from the second surface. Preferably, the axes of the various protuberances are substantially parallel. The exact shape of the protuberances, i.e. their cross-section, can be of any type and does not change the applicability of the present invention. Therefore, they can have a circular, oval, elliptical cross section, or even an irregular one. In a preferred embodiment of the invention, they have a frustoconical shape, therefore their cross-section changes in size (although the shape remains the same) along their longitudinal extension. The height of the different protuberances changes depending on the position in which they are located. As said, in correspondence of the arch of the foot, the height is at its maximum, and preferably is comprised between 5.5 mm and 7 mm. Preferably, in addition, in the remaining portion(s) of the midfoot region and of the hindfoot region the height of the protuberances is preferably comprised between 0.5 mm to 5 mm. Even more preferably, the protuberances have a third thickness, in correspondence of the heel region, the protuberances have the smallest height. In the heel region, the height of the protuberances is preferably comprised between 0.5 mm and 2 mm. Preferably, in the boundaries between the midfoot region and the forefoot region the height of the protuberances then decreases in "small steps" (e.g . small variations from the height of one protuberance to the subsequent one are present, for example preferably the change in height between two adjacent protuberances is comprised between 0.5 mm and 1 mm) along the longitudinal axis of the sole in order to smoothly join the midfoot region to the forefoot region in which no cushioning element is present. More preferably also the change between the maximum height in the arch region and the height present in the other region(s) of the midfoot and hindfoot is made gradually.

The combination of the first and second layer creates a sole element which has been studied to save the aesthetic features of the dress and/or business footwear: the size - in particular the thickness - of the combination of first and second layers is the same as standard, commonly used insole, but, through the above described special construction according to the invention, yields a comfort footwear that does not look like the standard "comfort shoe" known in the market, but as a classy dress and business shoe, without over-dimensioned - e.g. too thick which do not respect the fashionable proportions - elements.

Brief description of the drawings

Further features and advantages of a multi-layered sole according to the present invention will become more clearly apparent from the following detailed description thereof, given with reference to the accompanying drawings, where:

FIG. l shows a side view of a heeled footwear including the sole realized according to the present invention;

FIG. 2 shows a exploded side view of the sole realized according to the invention;

FIG. 3 shows a exploded side view of a portion of the sole of fig. 2; FIG. 4 shows a top view of a first layer of the sole of figs. 1-3;

FIG. 5 shows a bottom view of the first layer of fig . 4;

FIG. 5a shows an enlarged sectional view of a detail of the first layer of fig. 5;

FIG. 6 shows a sectional view along the line A'-A' of the first layer of figs. 4 and 5;

FIG. 7 shows a sectional view along the line B'-B' of the first layer of figs. 4 and 5;

FIG. 8 shows two perspective views from above and below of the first layer of figs. 4-7;

FIG. 9 shows a top view of a second layer of the sole of figs. 1-3; FIG. 10 shows a bottom view of the second layer of fig . 9;

FIG. 11 shows a side view of the second layer of figs. 9 and 10;

FIG. 12 shows two perspective views from above and below of the second layer of figs. 9-11;

FIG. 13 shows two perspective exploded views of the sole of fig . 3. Preferred embodiments of the invention

With initial reference to Fig. 1, a heeled footwear 100 including a multi- layered sole 1 realized according to an embodiment of the present invention is shown.

The depicted drawings are not in scale, in the same drawing some parts of the sole 1 can be enlarged with respect to the others to be shown in a clearer way. In addition, the depicted footwear 100 includes a sole 1 having a length of 270 mm, however the present invention is applicable to soles 1 having an arbitrary longitudinal length.

The multi-layered sole 1, depicted in an exploded view in figs. 2 and 3, comprises a first layer 2 and a second layer 3 that are sandwiched between an outsole 4 (not shown in fig . 2, but only in fig . 1), which is the layer in direct contact with the ground, and a liner 5, which is the layer in direct contact with the wearer foot. It is to be understood that liner and outsole can also be omitted from the present invention sole construction.

The second layer 3, shown in enlarged view and detached from the other layers in figs. 9-12, is the layer that enhances the stability of the footwear 1. In detail, the second layer 3 defines two surfaces 6,7, the first one 6 which is connected to the outsole, and the second one 7 which is in contact with the first layer and it includes a peripheral wall 8 which follows the edge of the second surface 7 of the layer 3 for the whole hindfoot region and for at least a portion of the midfoot region, preferably the wall is following the edge for 60% of the total length of the sole 1. The portion of the second surface 7 corresponding to the forefoot region on the contrary is smooth without protruding elements. The wall 8 defines a seat 8a in which a corresponding portion of the first layer 2 is received, as detailed below. The thickness T of the wall 6 is substantially preferably uniform and it is comprised between 5 mm and 6 mm, while the height of the wall is preferably comprised between a maximum reached at the hindfoot region comprised between 4 mm and 5 mm which gradually decreases to zero. This gradual change in height is visible clearly from the side view of fig. 11. Fig. 3 shows an exploded side view of the first and second layers according to the invention and an additional element, a shank 15. Indeed, the second layer 3 comprises, embedded in the hindfoot and midfoot region, the shank 15 that is positioned in a longitudinal step 15a (see fig. 11) formed on the first surface 7 of the second layer 3. As an example, the shank 15 can have a longitudinal length of 8 cm, a width of 2 cm and a depth of 2 mm. More in detail, the step 15a is located substantially in the middle of the hindfoot and midfoot regions of the first surface 6 of the second layer 3. The thickness of the step 15a is preferably comprised between 1.5 mm and 2.5 mm. The first surface 7 in correspondence of the forefoot region is substantially flat and smooth.

The total thickness of the second layer 3 varies depending on the considered region. In the flat portion corresponding to the forefoot region, the thickness is substantially uniform and preferably comprised between 0.8 mm and 1.2 mm, in this preferred example it is equal to 1 mm. From the end of the forefoot region or from the beginning of the midfoot region, the thickness of the second layer 3 gradually increases up to a thickness of between 9 mm and 12 mm at the heel region, including the step 15a and wall 8. In fig. 12 two perspective views from above and below of this second layer 3 are shown and the seat 8a and the step 15a are visible.

The first layer 2 allows an optimal distribution of the load weight in the footwear 100 and includes a first 9 and a second 10 surface, the first surface 9 being fixed to the liner 5, while the second surface 10 being in contact with the second layer 3.

The connection between the second layer 3 and the outsole 4 and/or the connection between the first layer 2 and the liner 5 can be made via gluing or by means of any other standard technique in the field . In addition, first and second layer 2,3 can be connected one to the other only in correspondence of their respective edges or they can also be glued in correspondence of their mating surfaces.

According to a characteristic of the invention, the first layer 2 comprises a specific padding/cushioning structure 12,11 which is partially inserted in the seat 8a formed by the peripheral wall 8.

The thickness of the first layer 2, outside the cushioning/padding 12,11 structure, is in this example equal to 1.5 mm. This is the thickness of the first layer 2 for example in correspondence of the forefoot region (with the exception of a pad below described), where the first and second surfaces 9, 10 are substantially flat and smooth.

FIG. 8 shows a perspective view of the first layer 2 according to the invention from above and below. From this view, the specific padding/cushioning structure 12, 11 can be better identified . The cushioning/padding structure, in correspondence on the forefoot region and possibly also partly in the midfoot region, more in particular in correspondence of the ball region, includes the pad 12, which is substantially a shock absorber insert located in the area where the metatarsal load is higher, due to the inclined position of the foot of the wearer wearing high heels. The pad 12 reduces the pressure on the forefoot and thus decreases the risk of joint irritations, increasing at the same time the comfort of the footwear. The pad 12 can be either fixed to one of the surfaces 9,10 of the first layer, for example by gluing, or molded together with the first layer 2 forming an integral piece. The pad is preferably placed in correspondence of the second surface 10, however can be also fixed in the opposite first surface 9. Alternatively, according to the depicted embodiment with a particular reference to fig. 5 and the sectional view along line A'-A' of the same depicted in fig . 6, the pad element 12 protrudes from both surfaces 9 and 10. The pad of the present embodiment has a maximum thickness comprised between 7 mm and 10 mm substantially at its center and its thickness continuously decreases to meet the flat portion of the first or second surface 9,10. Preferably, the maximum thickness of the pad 12 is comprised between 2.5 mm and 4 mm when considered as its maximum extension from the flat portion of the second surface 10, while it is comprised between 3 mm and 4.5 mm when considered as its maximum extension from the flat portion of the first surface 9. In the depicted embodiment, it extends respectively for 3.5 mm and 3 mm.

Additionally, the second surface 10 bears a specific cushioning element 11, in particular in correspondence of a portion of the hindfoot region and of the midfoot region. Although in the present drawing the cushioning element is fixed on the second surface 10 of the first layer 2, it can also be fixed to the first surface 9 or present in both sides.

With now reference to figs. 4, 6 and 8, the first layer 2 additionally can optionally include a walking support 23 to further enhance the comfort of the footwear 1. The walking support 23 is positioned in a portion of the first layer 2 along the edge of the layer 2 corresponding to the lateral side and substantially extends for a portion of the midfoot and of the forefoot region. The walking support may be in contact with the pad 12 and in this case in the contact region between the two, preferably the height of the pad and of the support should be substantially the same so as to form a continuous surface. The height of the walking support 23 is variable, as depicted in fig.4 and indicated with reference to positions E-F-G-H . Preferably, the height of the walking support is comprised between : 2 mm - 3.5 mm in E; 3 mm - 4.5 mm in F; 2 mm - 3.5 mm in G; 1.5 mm - 3 mm in H.

Preferably, the cushioning element 11 comprises a plurality of protuberances 13 - or pins - of different heights. More in detail, with now reference to figures 5, 5a and 7, the protuberances 13 can be for example cylinders (in the general meaning of cylinder, i.e. with any base), truncated cones (again with a generic cross section) or other solids projecting from the second surface 3 and having their axes substantially parallel one to the other. In the present example, the protuberances 13 have a conical shape and an oval cross-section, and the area of their cross section decreases from the base of the truncated cone at the second surface 10 to base at the end of the protuberance 13. The angle Ang . (see fig . 5a) formed at the base of the cone opposite to the surface 10 is in this example equal to 108°. The length of the major axis of the ellipsis forming the protuberances' cross section is preferably equal to 10 mm. In general the preferred range of the length of the major axis is between 9 mm and 11 mm.

The protuberances 13 are separated from one to the other by a distance comprised between 1 mm to 7 mm, i.e. preferably the protuberances are not in contact one to the other and an air gap is defined between any two protuberances 13. In the present embodiment, the distance between all protuberances is the same and equal to 1 mm, however the distance can be smaller or bigger and also can vary depending on the region of the first layer 2 under consideration .

According to a characteristic of the invention, the height of the different protuberances 13 (i.e. the height of the truncated cones) changes depending on the position in which they are located .

As shown in figs. 5 and 5a, in correspondence of the arch of the foot 22, the height of the protuberances 13 is at its maximum and it is preferably comprised between 5.5 mm and 7 mm. The protuberances 13 present in the region of the foot arch 22 are called 13A in fig . 5 and are depicted in an enlarged scale in fig . 5a.

The shortest protuberances 13 are those in correspondence of the heel 24 of the foot and are called 13D in figs. 5, 5a and 7. Their height is preferably comprised between 0.5 mm and 2 mm.

Preferably, in addition, in the remaining portions of the midfoot and hindfoot regions outside the arch 22 and heel 24 regions above described, the height of the protuberances 13 (in this case called 13B in figs. 5, 5a and 7) is substantially the same and it is preferably comprised between 3.5 mm and 5 mm, i.e. they have an intermediate third height between the heel protuberances' 13D height and the arch protuberances' 13A height. In fig. 7, which represents the section of fig. 5 along the B'-B' line, the protuberances 13D and 13B with their different heights can be clearly compared .

At the boundary between the forefoot and midfoot regions, preferably the height of the protuberances 13 decreases with respect to the height of protuberances 13B, and preferably this new fourth height of this boundary protuberances 13C is comprised between 1.5 mm and 3 mm in order to have a smooth connection between the midfoot and forefoot regions. From this area, going along the longitudinal axis of the sole 1, the height of the protuberances become equal to zero (i.e. no protuberance present) in order to smoothly join the forefoot region in which no cushioning element is present.

All the heights of the different protuberances 13A,13B,13D,13E are summarized in Table 1. However, it is to be understood that the protuberances can have even more than four different heights, i.e. they can have an arbitrary number of different heights, as long as there is an arch 22 support, i.e. the height of the protuberances is preferably highest in the arch region 22 thus defining a first height in the arch region and a second height elsewhere. More preferably, also a third height is defined, smaller than the first and the second, corresponding to protuberances 13A in the heel region 24.

Further, the first layer 2 comprises holes 14 (see figs. 4 and 8) with a diameter of about 1 mm for aeration. The holes 14 can be evenly distributed on the first layer 2 or, preferably, only in the midfoot and hindfoot region in combination with the protuberances 13. The fact that between two protuberances there is an empty volume filled with air favors the air circulation through the holes. These holes are also present in the liner 5.

The circulation of air can be also facilitated by the shape itself of the protuberances 13 : while walking the protuberances are compressed by the adjustment of the weight of the wearer and then they are decompressed in the subsequent walking movement. This action can be considered as a "pumping" action of air from the interstices between two protuberances 13 to the outside of the sole via the aeration holes 14.