referring to the drawings , there is shown an article of footwear 10 having an upper 11 secured to a sole unit 12 . in this arrangement , the sole unit comprises a footbed 13 , a midsole section 14 and an outsole section 15 . the footbed 13 is molded from a resilient plastics material such as polyurethane but other materials could also be used . in this arrangement , the midsole section is molded from a resilient plastics material such as eva but again other materials would be suitable . the outsole section 15 comprises a number of natural rubber or synthetic rubber outsole portions 16 but a continuous outsole could also be used , as could other materials . this particular rubber compound has a shore hardness of between 55 and 65 but other hardnesses could be employed depending on the required characteristics of the footwear . the use of separate outsole portions 16 can also lend itself to the provision of different materials in different parts of the outsole section 15 to produce varied wear / comfort characteristics . the midsole section 14 has a plurality of frusto - conical cavities 17 each of which has a small opening at its top end 18 and a wider opening at its bottom end 19 . in addition , there are a number of optional grooves 20 in the underside of the midsole section 14 , the grooves improving the flexibility of the sole unit in chosen areas and giving an element of decoration . the outsole portions 16 are securely bonded to the underside of the midsole section and the outsole portions 16 are shaped so as not to cover the grooves 20 . the parts of the outsole portions 16 which cover the bottom ends 19 of the cavities 17 are in the form of diaphragms 21 each of which connects to the surrounding part of outsole portion 16 by means of a peripherally extending portion 22 of reduced thickness . each reduced thickness portion 22 enables its enclosed diaphragm 21 to resiliently deflect more easily relative to its adjacent cavity 17 . the lowermost surface 23 of each diaphragm bulges downwardly so as to protrude below the surrounding parts of the outsole portion 16 . the underside of the footbed 13 has a concave recess 25 positioned above each cavity top end 18 and the recesses 25 are interconnected by means of a plurality of channels 26 formed in the underside of the footbed . in alternative embodiments the plurality of channels are provided in the upper surface of the midsole , or in both the underside of the footbed and the upper surface of the midsole . alternatively , as seen in fig8 and 9 , the plurality of channels 26 are provided in the underside of the footbed 13 and a plurality of corresponding channels 50 are provided in the upper surface of the midsole section 14 . also , cavities 52 may be provided in the footbed 13 in fluid communication with the channels 26 . a through orifice 27 is provided at each recess 25 to effect communication with the top side of the footbed . further orifices 28 are provided in the channels 26 . additional through orifices 54 may be provided to extend from cavities 52 in the footbed to the upper surface of the footbed 13 . the action of walking causes the diaphragms 21 to deform resiliently upwards into the cavities 17 and back again thereby pumping air from cavity to cavity via the channels 26 and recesses 25 . this action also causes air to flow through the orifices 27 and 28 to provide a ventilating effect within the upper 11 of the article of footwear . in on preferred embodiment , as seen in fig8 and 9 , the underside of the footbed 13 and the upper surface of the midsole section 14 are provided with a mating corrugated surfaces comprised of a plurality of interfitting ribs . the use of such a mating surface assists to keep alignment of the above described elements of the footbed 13 and the midsole section 14 . where mating corrugated surfaces are used , a constant depth of the channels 50 can be obtained by providing a plurality of channel structures 58 in the dips between ribs of the corrugated surface of the upper surface of the midsole section 14 . in more advanced embodiments , valve means may be provided to control the flow of air into and / or out of the cavities , or through the orifices 27 , 28 , or along the channels 26 . the valve means could be one - way mechanisms or could rely on compressive closure of the openings due to weight transfer during the walking cycle . one example of a sole unit having a valve arrangement is shown in fig4 to 6 . the heel area of the sole unit incorporates an air inlet member 40 which is located generally in the midsole section 14 and which extends laterally in this embodiment . the inlet member 40 is generally tubular and is open to the atmosphere at one or both of its lateral ends 43 . the inside of the inlet member 40 communicates with two of the cavities 17 in the heel area via one - way valves 41 . in this embodiment the one - way valves 41 are in the form of “ duck - bill ” valves but other types of valves are envisaged . air can therefore be drawn into the cavities 17 by suction when the diaphragms 21 deform resiliently downwards . the cavities 17 also have one - way valves 42 which control communication with the recesses 25 / channels 26 . again , in this example the one - way valves 42 are “ duck - bill ” valves which are ideally carried by the inlet member 40 . fresh air drawn into the cavities 17 as the diaphragms 21 deform downwards is then passed outwardly through the valves 42 when the diaphragms 21 deform upwardly into the cavities 17 . this fresh air is distributed around the sole unit and out through orifices 27 and 28 ( not shown in fig5 and 6 ). this passage of air can assist ventilation of the shoe and / or can provide a cooling action and / or can assist in the dispersal of moisture and / or odor . the precise form and location of the valve system is a matter of design choice and could be provided for more cavities than the two shown . the inlet member and valves need not be separate components but could be molded as part of the midsole . in other embodiments , the diaphragms 21 could be formed of a transparent or semi - transparent material such that the inside of the cavities / underside of the footbed can be seen . contrasting colors in the cavity could produce a desirable decorative effect . it will be appreciated that the number of cavities could vary as could their precise shape . also , the reduced thickness portions 22 which define the shapes of the diaphragms could be omitted or partially omitted if the material of the outsole was already sufficiently flexible . the footbed could be omitted in some types of footwear , for example where an insole is lasted to the upper in which case the midsole would be secured to the lasting margin of the upper . other modifications will be apparent without departing from the scope of the attached claims .
there is provided a sole unit having a midsole section and an outsole section . the midsole incorporates a number of cavities which open at their top ends and which are wider at their bottom ends . the outsole section incorporates a number of diaphragm elements which close off the bottoms of the cavities . in some arrangements there is a footbed which has in its underside a number of recesses disposed above each of the cavities , the recesses being linked by channels and incorporating orifices leading to the inside of an article of footwear .