Patent Publication Number: US-2022218068-A1

Title: Article of footwear having a sole structure with a fluid-filled chamber

Description:
BACKGROUND 
     Articles of footwear generally include two primary elements: an upper and a sole structure. The upper is often formed from a plurality of material elements (e.g., textiles, polymer sheet layers, polymer foam layers, leather, synthetic leather) that are stitched or adhesively bonded together to form a void within the footwear for comfortably and securely receiving a foot. More particularly, the upper forms a structure that extends over instep and toe areas of the foot, along medial and lateral sides of the foot, and around a heel area of the foot. The upper may also incorporate a lacing system to adjust the fit of the footwear, as well as permitting entry and removal of the foot from the void within the upper. In addition, the upper may include a tongue that extends under the lacing system to enhance adjustability and comfort of the footwear, and the upper may incorporate a heel counter for stabilizing the heel area of the foot. 
     The sole structure is secured to a lower portion of the upper and positioned between the foot and the ground. In athletic footwear, for example, the sole structure often includes a midsole and an outsole. The midsole may be formed from a polymer foam material that attenuates ground reaction forces (i.e., provides cushioning) during walking, running, and other ambulatory activities. The midsole may also include fluid-filled chambers, plates, moderators, or other elements that further attenuate forces, enhance stability, or influence the motions of the foot, for example. In some configurations, the midsole may be primarily formed from a fluid-filled chamber. The outsole forms a ground-contacting element of the footwear and is usually fashioned from a durable and wear-resistant rubber material that includes texturing to impart traction. The sole structure may also include a sockliner positioned within the void of the upper and proximal a lower surface of the foot to enhance footwear comfort. 
     One manner of reducing the weight of a polymer foam midsole and decreasing the effects of deterioration following repeated compressions is disclosed in U.S. Pat. No. 4,183,156 to Rudy, hereby incorporated by reference, in which ground reaction force attenuation is provided by a fluid-filled bladder formed of an elastomeric materials. The bladder includes a plurality of tubular chambers that extend longitudinally along a length of the sole structure. The chambers are in fluid communication with each other and jointly extend across the width of the footwear. The bladder may be encapsulated in a polymer foam material, as disclosed in U.S. Pat. No. 4,219,945 to Rudy, hereby incorporated by reference. The combination of the bladder and the encapsulating polymer foam material functions as a midsole. Accordingly, the upper is attached to the upper surface of the polymer foam material and an outsole or tread member is affixed to the lower surface. Bladders of the type discussed above are generally formed of an elastomeric material and are structured to have an upper and lower portions that enclose one or more chambers therebetween. The chambers are pressurized above ambient pressure by inserting a nozzle or needle connected to a fluid pressure source into a fill inlet formed in the bladder. Following pressurization of the chambers, the fill inlet is sealed and the nozzle is removed. 
     Fluid-filled bladders suitable for footwear applications may be manufactured by a two-film technique, in which two separate polymer sheets are bonded together to form a periphery of a bladder, and the sheets are also bonded together at predetermined interior areas to give the bladder a desired configuration. That is, the interior bonds provide the bladder with chambers having a predetermined shape and size. In another method, often referred to as thermoforming, two separate polymer sheets are heated, molded to a predetermined shape, and bonded together to form a periphery and interior bonds of the bladder. Such bladders have also been manufactured by a blow-molding technique, wherein a molten or otherwise softened elastomeric material in the shape of a tube is placed in a mold having the desired overall shape and configuration of the bladder. The mold has an opening at one location through which pressurized air is provided. The pressurized air induces the liquefied elastomeric material to conform to the shape of the inner surfaces of the mold. The elastomeric material then cools, thereby forming a bladder with the desired shape and configuration. 
     SUMMARY 
     According to one configuration, an article of footwear has an upper and a sole structure secured to the upper. The sole structure includes a chamber that encloses a pressurized fluid. The chamber has a first surface, a second surface, and a sidewall surface. The first surface is oriented to face toward upper, the second surface is located opposite the first surface and oriented to face away from the upper, and the sidewall surface extends between the first surface and the second surface and around at least a portion of the chamber. The first surface and the second surface define a plurality of elongated subchambers oriented in a direction that extends between a lateral side of the footwear and an opposite medial side of the footwear. The first surface and the second surface are joined to each other between at least two of the subchambers to form a bond oriented in the direction that extends between the lateral side of the footwear and the medial side of the footwear. End areas of the bond are spaced from the sidewall surface. The second surface defines an indentation at the bond, the indentation extending past the ends areas of the bond such that the indentation extends entirely across the chamber and from a portion of the sidewall surface located on the lateral side of the footwear to a portion of the sidewall surface located on the medial side of the footwear. 
     According to another configuration, an article of footwear has an upper and a sole structure secured to the upper. The sole structure includes a chamber that encloses a pressurized fluid. The chamber includes a plurality of tubes oriented in a direction that extends between a lateral side of the footwear and an opposite medial side of the footwear. A diameter of the tubes decreases in a direction from a heel region of the chamber to a forefoot region of the bladder. 
     According to a further configuration, an article of footwear includes an upper and a sole structure secured to the upper. The sole structure includes a chamber that encloses a pressurized fluid. The chamber includes subchambers laterally extending in a direction that extends between a lateral side of the footwear and an opposite medial side of the footwear. A bottom surface of the chamber includes at least one bond that extends in the direction that extends between the lateral side of the footwear and the medial side of the footwear. The bond forming an indentation in the bottom surface that separates one subchamber from an adjacent subchamber. An outsole defines a ground engaging surface that forms a plurality of outwardly-projecting ground engaging members, with the outsole extending into the indentation. The outsole includes a first area including the ground engaging members and a second area located where the outsole extends into the indentation, wherein the ground engaging members are absent from the second area. 
     According to yet another configuration, an article of footwear has an upper and a sole structure secured to the upper. The sole structure includes a chamber that encloses a pressurized fluid. The chamber includes a plurality of subchambers oriented in a direction that extends between a lateral side of the footwear and an opposite medial side of the footwear. A cross-sectional size of the subchambers decreases in a direction from a heel region of the chamber to a forefoot region of the chamber. 
     The advantages and features of novelty characterizing aspects of the invention are pointed out with particularity in the appended claims. To gain an improved understanding of the advantages and features of novelty, however, reference may be made to the following descriptive matter and accompanying figures that describe and illustrate various configurations and concepts related to the invention. 
    
    
     
       FIGURE DESCRIPTIONS 
       The foregoing Summary and the following Detailed Description will be better understood when read in conjunction with the accompanying figures. 
         FIG. 1  is a perspective view of an article of footwear. 
         FIG. 2  is an exploded perspective view of the article of footwear. 
         FIG. 3  is a perspective view of a fluid-filled chamber from the article of footwear. 
         FIG. 4  is a top plan view of the fluid-filled chamber. 
         FIG. 5  is a bottom plan view of the fluid-filled chamber. 
         FIG. 6  is a side elevational view of the fluid-filled chamber. 
         FIG. 7  is a cross-sectional view of the fluid-filled chamber, as defined by section line  7 - 7  in  FIG. 5 . 
         FIG. 8  is an exploded perspective view of the fluid-filled chamber. 
         FIG. 9A  is a cross-sectional view of the chamber after the chamber has been molded, as defined by section line  9 - 9  in  FIG. 3 . 
         FIG. 9B  is a cross-sectional view of the chamber of  FIG. 9A  after it has been inflated with fluid. 
         FIG. 10A  is a side view of a molding apparatus used in a process for manufacturing a fluid-filled chamber. 
         FIG. 10B  is a side view of a molding apparatus used in a process for manufacturing a fluid-filled chamber including an insert. 
         FIG. 10C  is a side view of a molding apparatus used in a process for manufacturing a fluid-filled chamber including barrier layers. 
         FIG. 10D  is a side view of a molding apparatus used in a process for manufacturing a fluid-filled chamber after the apparatus has been closed. 
         FIG. 10E  is a perspective view of a product of a molding apparatus. 
         FIG. 11  is a top view of a further configuration of a fluid-filled chamber. 
         FIG. 12  is a top view of a further configuration of a fluid-filled chamber. 
         FIG. 13  is a top view of a further configuration of a fluid-filled chamber. 
         FIG. 14  is a top view of a further configuration of a fluid-filled chamber. 
         FIG. 15  is a bottom view of another fluid-filled chamber. 
         FIG. 16  is a side view of another article of footwear. 
     
    
    
     DETAILED DESCRIPTION 
     The following discussion and accompanying figures disclose various configurations of an article of footwear. Although the footwear is disclosed as having a configuration that is suitable for running, concepts associated with the footwear may be applied to a wide range of athletic footwear styles, including basketball shoes, cross-training shoes, football shoes, golf shoes, hiking shoes and boots, ski and snowboarding boots, soccer shoes, tennis shoes, and walking shoes, for example. Concepts associated with the footwear may also be utilized with footwear styles that are generally considered to be non-athletic, including dress shoes, loafers, and sandals. Accordingly, the concepts disclosed herein may be utilized with a variety of footwear styles. 
     General Footwear Structure 
     An article of footwear  100  is depicted in  FIGS. 1 and 2  as including an upper  110  and a sole structure  120 . Upper  110  provides a comfortable and secure covering for a foot of a wearer. As such, the foot may be located within upper  110  to effectively secure the foot within footwear  100 . Sole structure  120  is secured to a lower area of upper  110  and extends between upper  110  and the ground. When the foot is located within upper  110 , sole structure  120  extends under the foot to attenuate ground reaction forces (i.e., cushion the foot), provide traction, enhance stability, and influence the motions of the foot, for example. 
     Upper  110  is depicted as having a substantially conventional configuration formed from a variety of elements (e.g., textiles, polymer sheet layers, polymer foam layers, leather, synthetic leather) that are stitched, bonded, or otherwise joined together to provide a structure for receiving and securing the foot relative to sole structure  120 . The various elements of upper  110  define a void  102 , which is a generally hollow area of footwear  100  with a shape of the foot, that is intended to receive the foot. As such, upper  110  extends along the lateral side  104  of the foot, along the medial side  106  of the foot, over the foot, around a heel of the foot, and under the foot. Access to void  102  is provided by an ankle opening  103  located in at least the heel of the footwear  100 . A lace  105  extends through various lace apertures  107  and permits the wearer to modify dimensions of upper  110  to accommodate the proportions of the foot. More particularly, lace  105  permits the wearer to tighten upper  110  around the foot, and lace  105  permits the wearer to loosen upper  110  to facilitate entry and removal of the foot from void  102  (i.e., through ankle opening  103 ). As an alternative to lace apertures  107 , upper  110  may include other lace-receiving elements, such as loops, eyelets, hooks, and D-rings. In addition, upper  110  includes a tongue  108  that extends between void  102  and lace  105  to enhance the comfort and adjustability of footwear  100 . In some configurations, upper  110  may incorporate other elements, such as reinforcing members, aesthetic features, a heel counter that limits heel movement in the heel of the footwear, a wear-resistant toe guard located in the forefoot of the footwear, or indicia (e.g., a trademark) identifying the manufacturer. Accordingly, upper  110  is formed from a variety of elements that form a structure for receiving and securing the foot. 
     Turning to  FIG. 2 , the primary elements of sole structure  120  are a midsole  122  and an outsole  124 . Midsole  122  may include, for example, a sealed fluid-filled chamber  200 , which will be discussed below, and encloses a pressurized or unpressurized fluid. Although not depicted, midsole  122  may also include, for example, a polymer foam material, such as polyurethane or ethylvinylacetate, that is located above and/or below chamber  200 . In addition to the fluid-filled chamber  200  and the polymer foam material, midsole  122  may incorporate one or more additional footwear elements that enhance the comfort, performance, or ground reaction force attenuation properties of footwear  100 , including plates, moderators, lasting elements, or motion control members, for example. Although absent in some configurations, outsole  124  is secured to a lower surface of midsole  122  and may be formed from a rubber material that provides a durable and wear-resistant surface for engaging the ground. In addition, outsole  122  may be textured to enhance the traction (i.e., friction) properties between footwear  100  and the ground. The sole structure  120  may further include a sockliner (not shown), which is a compressible member located within void  102  and adjacent a lower surface of the foot to enhance the comfort of footwear  100 . 
     Chamber Configuration 
       FIG. 3  shows a perspective view of an exemplary configuration of chamber  200 . When incorporated into footwear  100 , chamber  200  may have a shape that fits within a perimeter of midsole  122  and substantially extends from forefoot region to heel region and also from lateral side  104  to medial side  106 , thereby corresponding with a general outline of the foot. When a foot is located within upper  110 , chamber  200  extends under substantially all of the foot in order to attenuate ground reaction forces that are generated when sole structure  120  is compressed between the foot and the ground during various ambulatory activities, such as running and walking. In other configurations, chamber  200  may extend under only a portion of the foot. As depicted in  FIG. 1 , chamber  200  forms a majority of an exposed side surface of sole structure  120 . In other configurations, however, a polymer foam material of midsole  122  may extend entirely around chamber  200  and form the exposed side surface of midsole  122 . 
     For purposes of reference in the following discussion, chamber  200  may be divided into three general regions: a forefoot region  206 , a midfoot region  204 , and a heel region  202 . Forefoot region  206  generally includes portions of chamber  200  corresponding with the toes and the joints connecting the metatarsals with the phalanges. Midfoot region  204  generally includes portions of chamber  200  corresponding with an arch area of the foot. Heel region  202  generally corresponds with rear portions of the foot, including the calcaneus bone. Chamber  200  has a medial side  208  and an opposite lateral side  210 , which may extend through each or regions  202 ,  204 , and  206  and correspond with opposite sides of chamber  200 . More particularly, lateral side  210  corresponds with an outside area of the foot (i.e. the surface that faces away from the other foot), and medial side  208  corresponds with an inside area of the foot (i.e., the surface that faces toward the other foot). Regions  202 ,  204 ,  206  and sides  208 ,  210  are not intended to demarcate precise areas of chamber  200 . Rather, regions  202 ,  204 ,  206  and sides  208 ,  210  are intended to represent general areas of chamber  200  to aid in the following discussion. 
     Chamber  200  includes an upper barrier layer  292  and a lower barrier layer  294  that are substantially impermeable to a pressurized fluid contained by chamber  200 . Whereas upper barrier layer  292  forms a first or upper surface of chamber  200 , lower barrier layer  294  forms a second or lower surface of chamber  200 . Additionally, upper barrier layer  292  extends downward to form a side surface or sidewall  295  of chamber  200 . Sidewall  295  may, for example, form an exposed sidewall of sole structure  120 . Moreover, upper barrier layer  292  and lower barrier layer  294  are bonded together around their respective peripheries to form a peripheral bond  296  adjacent to the lower surface of chamber  200 . In configurations where lower barrier layer  294  forms sidewall  295 , peripheral bond  296  may be located adjacent to the upper surface of chamber  200 . 
     Peripheral bond  296  joins barrier layers  292  and  294  around the periphery of chamber  200  to form a sealed structure having an interior void or cavity, in which the pressurized fluid is located. The pressurized fluid contained by chamber  200  may induce an outward force upon barrier layers  292  and  294  that tends to separate or otherwise press outward upon barrier layers  292  and  294 , thereby distending barrier layers  292  and  294 . In order to restrict the degree of outwardly-directed swelling (i.e., distension) of barrier layers  292  and  294  due to the outward force of the pressurized fluid, a plurality of interior bonds  230  are formed between barrier layers  292  and  294 , which will be discussed below. 
     A wide range of polymer materials may be utilized for chamber  200 , specifically barrier layers  292  and  294 . In selecting materials for chamber  200 , engineering properties of the material (e.g., tensile strength, stretch properties, fatigue characteristics, dynamic modulus, and loss tangent) as well as the ability of the material to prevent the diffusion of the fluid contained by chamber  200  may be considered. When formed of thermoplastic urethane, for example, chamber  200  may have a thickness of approximately 1.0 millimeter, but the thickness may range from 0.2 to 4.0 millimeters or more, for example. In addition to thermoplastic urethane, examples of polymer materials that may be suitable for chamber  200  include polyurethane, polyester, polyester polyurethane, and polyether polyurethane. Chamber  200  may also be formed from a material that includes alternating layers of thermoplastic polyurethane and ethylene-vinyl alcohol copolymer, as disclosed in U.S. Pat. Nos. 5,713,141 and 5,952,065 to Mitchell, et al. A variation upon this material may also be utilized, wherein layers include ethylene-vinyl alcohol copolymer, thermoplastic polyurethane, and a regrind material of the ethylene-vinyl alcohol copolymer and thermoplastic polyurethane. Another suitable material for chamber  200  is a flexible microlayer membrane that includes alternating layers of a gas barrier material and an elastomeric material, as disclosed in U.S. Pat. Nos. 6,082,025 and 6,127,026 to Bonk, et al. Additional suitable materials are disclosed in U.S. Pat. Nos. 4,183,156 and 4,219,945 to Rudy. Further suitable materials include thermoplastic films containing a crystalline material, as disclosed in U.S. Pat. Nos. 4,936,029 and 5,042,176 to Rudy, and polyurethane including a polyester polyol, as disclosed in U.S. Pat. Nos. 6,013,340; 6,203,868; and U.S. Pat. No. 6,321,465 to Bonk, et al. 
     The fluid within chamber  200  may be pressurized between zero and three-hundred-fifty kilopascals (i.e., approximately fifty-one pounds per square inch) or more. In addition to air and nitrogen, the fluid may include octafluorapropane or be any of the gasses disclosed in U.S. Pat. No. 4,340,626 to Rudy, such as hexafluoroethane and sulfur hexafluoride. In some configurations, chamber  200  may incorporate a valve or other structure that permits the wearer to adjust the pressure of the fluid. 
     Chamber  200  includes various elements, including a plurality of elongated subchambers  220 , a peripheral subchamber  224 , and various interior bonds  230 . Whereas peripheral subchamber  224  extends around a periphery of chamber  200  and forms the sidewall of sole structure  120 , subchambers  220  extend across bladder  200  and join with opposite sides of peripheral subchamber  224 . In other words, subchambers  220  extend between peripheral subchamber  224  and may be fluidically connected with peripheral subchamber  224 . Moreover, interior bonds  230  extend between subchambers  220  and separate the fluid in adjacent subchambers  220  from each other. Chamber  200  may also include a sealed conduit  250 , through which the fluid enclosed within chamber  200  has bee supplied, as will be discussed below. 
     Chamber  200  may contain one or more interior bonds  230 . Interior bonds  230  may assist in forming an overall structure of the chamber  200 . For example, in the absence of the interior bonds, the outward force induced by the pressurized fluid within chamber  200  would impart a rounded or otherwise bulging configuration to chamber  200 , particularly in areas corresponding with the upper surface or upper barrier  292  and the lower surface or lower barrier  294 . Such interior bonds  230  may be spaced inward sidewall  295 , such as where peripheral bond  296  is located, and may be distributed throughout chamber  200 . As a result, interior bonds may restrict the degree of outwardly-directed swelling or distension of barrier layers  292  and  294  and retain the intended contours of the upper surface and the lower surface provided by barrier layers  292  and  294 . 
     Interior bonds  230  may exhibit a variety of configurations within the scope of the present invention. In heel region  202 , the indentations formed by interior bonds  230  may have a greater depth than in forefoot region  206  due to the increased overall thickness of chamber  200  in heel region  202 . In addition, the area of each interior bond  230  in heel region  202  is generally greater than the area of each interior bond  230  in forefoot region  206 . The position of interior bonds  230  with respect to surfaces provided by upper barrier layer  292  and lower barrier layer  294  may also vary. For example, interior bonds  230  may be positioned so as to be closer to an upper surface provided by upper barrier layer  292 , midway between upper and lower surfaces provided by barrier layers  292  and  294 , or at a position that is closer to a lower surface provided by lower barrier layer  294 . 
     Interior bonds  230  are formed between barrier layers  292  and  294  and separate one or more of subchambers  220  that enclose and contain the fluid of chamber  200 . Subchambers  220  can provide areas filled with the pressurized fluid of chamber  200  that provide a shape that corresponds to a wearer&#39;s foot and cushion and support the foot. As shown in the example of  FIG. 3 , chamber  200  may include subchambers  220  in any of regions  202 ,  204 , and  206 . Subchambers  220  may cross chamber  200  and generally extend between opposite portions of peripheral subchamber  224 , thereby generally extending between medial side  208  and lateral side  210  of chamber  200 . 
     Subchambers  220  may also be provided in different numbers than shown in the example of  FIG. 3 . For example, heel region  202 , midfoot region  204 , and forefoot region  206  may have different numbers of subchambers than shown in  FIG. 3 . As shown in  FIG. 3 , subchambers  220  have an elongated shape with a longitudinal axis extending in a direction between medial side  208  and lateral side  210 . In another configuration, the shapes and geometries may vary from subchamber to subchamber. For example, as shown in  FIG. 3 , a connecting portion  222  may connect subchambers  220  together, with connecting portion  222  sealed to enclose pressurized fluid, like subchambers  220 . Connecting portion  222  may be provided between other subchambers of chamber  200  or no connecting portion  222  may be included in chamber  200 . 
     Internal bonds  230  extend laterally (i.e., in a direction extending between sides  208  and  210 ) and separate subchambers  220  from one another in a heel to forefoot direction of chamber  200 . In different configurations of chamber  200 , internal bonds  230  may vary in size, shape, or number. For example, internal bond  231  and internal bond  232  may separate portions of subchamber  220  from portions of an adjacent subchamber  220 , such as when connecting portion  222  is provided, with internal bond  231  and internal bond  232  being located laterally of connecting portion  222  in a direction extending between medial side  208  and lateral side  210 . 
     Although chamber  200  includes the various subchambers  220  discussed above, chamber  200  may also include a variety of other inflated structures. For example, chamber  200  may include inflated portion  226  in forefoot region  206  that has a generally polygonal shape or other desired shape to provide cushioning and support in forefoot region  206 . To provide the shape of inflated portion  226 , a bond  233  may be provided in chamber  200 . 
     As shown in  FIG. 4 , peripheral subchamber  224  may substantially extend around the periphery of chamber  200  with an interruption at the toe in forefoot region  206 . In another configuration, peripheral subchamber  224  may continuously extend around the periphery of chamber  200  without interruption. Peripheral subchamber  224  may extend around and be fluidically connected to subchambers  220  in heel region  202 , midfoot region  204 , and forefoot region  206 . Such a structure may be implemented, for example, by providing internal bonds  230  that extend only a portion of a distance between medial side  208  and lateral side  210  so that internal bonds  230  do not extend completely from an edge at medial side  208  to an edge at lateral side  210 . Similarly to the subchambers  220 , peripheral subchamber  224  may provide a sealed area of pressurized fluid that cushions and supports a wearer&#39;s foot. In some configurations, peripheral subchamber  224  may extend upwards towards upper  110  of footwear  100  to a greater extent than subchambers  220  and/or may slope downwards towards a central portion of chamber  200  to provide a shape that may conform to a wearer&#39;s foot. 
     Although the configuration of chamber  200  may vary considerably, chamber  200  may include bonded areas or other features where no regions of pressurized fluid are present. As shown in  FIGS. 4 and 5 , chamber  200  may include bond area  234 . Such bonded areas may be provided in any number as may be necessary to provide a desired shape and/or amount of cushioning for a wearer&#39;s foot and may be provided in different shapes and in different locations of chamber  200  than shown in the example of  FIG. 5 . In another example, chamber  200  need not include any bonded area  203 . 
     As shown in the example of  FIG. 5 , which depicts a bottom view of chamber  200 , internal bonds  230  might be arranged to extend across a portion of the width of chamber  200  in a direction between medial side  208  and lateral side  210  of chamber  200 . For example, internal bonds  230  may extend laterally across only a portion of the width of chamber  200  in a direction between medial side  208  and lateral side  210  on the bottom surface of chamber  200 . As a result, the subchambers  220  separated by these internal bonds  230  may be joined at their ends because the internal bonds extend across only a portion of the width of chamber  200 . For example, ends of subchambers  220  on lateral side  210  of chamber  200  may be joined by joining portion  228  while ends of subchambers  220  on medial side  208  of chamber  200  may be joined by joining portion  229  on the bottom surface of chamber  200 . Such joining portions  228 ,  229  may fluidically join subchambers  220 . Joining portions  227 ,  229  may provide support to a wearer&#39;s foot but may also limit the flexibility provided by internal bonds to chamber  200  because joining portions  227 ,  229  may not bend as readily as internal bonds  230 , for example, which may have a smaller thickness than joining portions  227 ,  229 . 
     Flexibility of sole structure  120 , including chamber  200 , is a common design consideration due to the forces exerted upon footwear  100  while footwear  100  is worn. For example, during running or walking, sole structure  120  generally flexes or otherwise bends to accommodate the natural flexing of the foot, particularly in forefoot region  206  of chamber  200 . The bonds provided in a bladder might not only serve to provide shape to inflated regions, such as subchambers, but may also provide flexibility to a bladder. For example, internal bonds  230  may provide areas with a degree of flexibility between subchambers  220 . Such internal bonds  230  may provide a degree of flexibility by providing areas of a chamber  200  with a reduced thickness due to the joining of the upper and lower barrier layers  292  and  294  together. 
     Various indentations  240  may be provided on a bottom surface of chamber  200 . Such an arrangement may provide increased flexibility to the bottom surface of a bladder. Indentations  240  may extend from end portion or area  235  of internal bonds  230  to sidewall  295  or other side edges of chamber  200  in a direction towards medial side  208  and towards lateral side  210 , as shown in  FIG. 5 . For example, an indentation  240  may extend past an end area  235  of internal bond  230  nearest medial side  208  and extend to the edge of chamber  200  on medial side  208 . Similarly, an indentation  240  may extend past an end area  235  of internal bond  230  nearest lateral side  210  and extend to the edge of chamber  200  on lateral side  210 . Indentations  240  may be formed in chamber  200  as indentations in a bottom surface of peripheral subchamber  224  so that peripheral subchamber  224  has a reduced thickness where indentations  240  are located. 
     Such an internal bond structure may be provided to impart increased flexibility on the bottom surface of the chamber, such as by providing an area of decreased bladder thickness due to the joined surfaces of the upper barrier layer and the lower barrier layer and due to the indentations in the bottom surface of the chamber. Given that the degree of force necessary to bend an object is generally dependent upon the thickness of the object, the reduced thickness of chamber  200  in the areas of internal bonds facilitates flexing during movement of a wearer of footwear  100  that includes chamber  200  in its sole structure  120 . 
     Indentations  240  may be configured so that subchambers  220  are separated into pairs. As shown in the example of  FIG. 5 , some internal bonds  230  are located adjacent to, or connected with, indentations  240  and other internal bonds  230  are not adjacent to, or connected with, indentations  240 . Internal bonds  230  located adjacent to, or connected with, indentations  240  may alternate with other internal bonds  230  not adjacent to, or connected with, indentations  240 . Such alternation of indentations  240  and bonds  230  without indentations  240  may extend in a heel to toe direction on the bottom surface of chamber  200 , as shown in  FIG. 5 . As a result, internal bonds  230  and indentations  240  may cooperate to separate subchambers  220  from one another, so that subchambers  220  form subchamber pairs  260 . 
     As shown in  FIG. 5 , subchamber pairs  260  may be separated from one another by internal bond  230  and indentations  240  that laterally extend towards medial side  208  and lateral side  210 . In other words an internal bond  230  and an indentation  240  at each end of internal bond  230  may cooperate to form a recess extending entirely across the width of the bottom surface of chamber  200  of chamber  200  from lateral side  210  to medial side  208 . Internal bonds  230  and indentations  240  also form a portion of a sidewall surface of chamber  200  located on lateral side  210  of the footwear and form a portion of a sidewall surface located on medial side  208  of the footwear, such as by forming indentations in the sidewall surfaces. Such an arrangement of subchamber pairs separated by internal bonds with laterally extending indentations advantageously provides a chamber structure with areas that support and cushion a wearer&#39;s foot, such as the subchamber pairs, while also providing increased flexibility and movement to the bladder, such as between the subchamber pairs where internal bonds with laterally extending indentations are located. 
     According to another example, internal bonds  230  between subchambers  220  may have a substantially continuous shape along a direction in which the internal bond extends. For instance, although  FIG. 5  shows that internal bonds  230  and laterally extending indentations  240  may have different shapes, internal bonds  230  and indentations  240  may instead have a substantially continuous shape and/or size in a direction extending laterally between medial side  208  and lateral side  210 . More particularly, the size and shape of subchambers  220 , internal bonds  230 , and indentations  240  may be the same or different. 
     In contrast with internal bonds  230 , for example, indentations  240  on the bottom surface of chamber  200  do not join upper barrier layer  292  and lower barrier layer  294  of chamber  200 . For example, as shown in  FIG. 6 , indentations  240  are located in the bottom surface of chamber  200  provided by lower barrier layer  294 , which increase the flexibility of chamber  200  by providing areas where chamber  200  preferentially bends. Indentations  240  may have, for example, a depth  9  that is a portion of a thickness of chamber  200 . The thickness of chamber may be measured along the same direction as depth  9 , namely between a top surface of chamber  200  facing upper  110  and a bottom surface facing outsole  140 . Depth  9  of indentations  240  may be, for example, 10-90% of the thickness of chamber  200 . In another example, depth  9  of indentations  240  may be approximately 50% or more of the thickness of chamber  200 . In a further example, depth  9  of indentations  240  may be approximately 50-90% of the thickness of chamber  200 . Providing indentations  240  that have a depth  9  of approximately 50% or more of the thickness of chamber  200  may advantageously enhance the flexibility of chamber  200 . 
     However, indentations  240  do not join upper barrier layer  292  to lower barrier layer  294  of chamber  200  where indentations  240  are located. As a result, there may be fluid-filled portions  242  located above indentations  240  in a direction extending between the lower barrier layer  294  to the upper barrier layer  292  so that there are fluid-filled portions  242  of chamber  200  between the indentations  240  and the upper barrier layer  292 , as shown in  FIG. 6 . Thus, chamber  200  may simultaneously accommodating flexing and providing ground reaction force attenuation. 
     Fluid-filled portions  242  provided between indentations  240  and upper barrier layer  292  may be fluidically connected by peripheral chamber  224 . Although indentations  240  may provide interruptions for peripheral chamber  224  on the bottom surface of chamber  200 , as shown in  FIG. 5 , peripheral chamber  224  may extend over indentations  240  to connect fluid-filled portions  242  along a side surface and along a top surface of chamber  200 , as shown in  FIGS. 4 and 6 . 
     Subchambers  220  of chamber  200  may vary in shape and/or size from one subchamber to another. The size or diameter of a subchamber  220  may be measured between a bottom surface and a top surface of chamber  200 , which is also a direction  7  for measuring a thickness of subchamber  200 . For example, a rearmost subchamber  220  in heel region  202  may have a size 5 along the thickness direction of chamber  200 , while a chamber in the furthest tip of forefoot region  206  has a size 6. 
     The size of subchambers  220  may vary from heel region  202  to forefoot region  206  along direction  8 , with size 5 being larger than size 6. Such a variation of subchamber  220  size may provide chamber  200  with a thickness  7  that generally tapers from heel to forefoot and generally conforms to a shape of a foot. For example, subchambers  220  in heel region  202  may be larger than subchambers  220  in midfoot region  204  and forefoot region  206 . In another example, subchambers  220  may decrease in size from one subchamber to the next adjacent subchamber. As shown in the example of  FIG. 7 , a distance may be measured from a center of one subchamber to a center of an adjacent subchamber, such as distance  1  from a center of a subchamber  220  to a center of subchamber  220 , distance  2  from a center of subchamber  220  to another, distance  3  from a center of subchamber  220  to another, and distance  4  from subchamber  220  to another. 
     Subchambers  220  may decrease in size or diameter from midfoot region  204  to forefoot region  206 . As a result, the distance between adjacent subchambers may decrease in a direction towards the toe, with distance  1  being greater than distance  2 , distance  2  being greater than distance  3 , and distance  3  being greater than distance  4 . 
     A chamber, such as chamber  200 , may include one or more reinforcement members to provide additional strength to the chamber. A reinforcement member may be made of a different material than the remainder of the bladder, such as the upper and lower barrier layers of a chamber. U.S. Pat. No. 7,665,230 describes a reinforcement member and is hereby incorporated by reference in its entirety. As shown in the example of  FIGS. 8, 9A, and 9B , chamber  200  includes a reinforcement member  270  as a separate piece that is bonded or otherwise secured to chamber  200 . In general, reinforcement member  270  generally extends around portions and the periphery of chamber  200 . The material forming reinforcement member  270  may exhibit a greater modulus of elasticity than the material forming chamber  200 . Accordingly, the configuration and material properties of reinforcing reinforcement member  270  may impart reinforcement to sole structure  120  that includes chamber  200 . 
     Upper portion  272  of reinforcing member  270  may extend along both the medial side  208  and lateral side  210  of chamber  200  and provide a defined lasting margin for securing upper  110  to sole structure  120  during the manufacture of footwear  100 . One issue with some sole structures is that the precise extent to which the upper should be secured to the sole structure is not evident from the configuration of the sole structure. Referring to the cross-section of  FIG. 9A , which shows a cross-sectional view of chamber  200  after chamber  200  has been molded but before inflation with fluid, reinforcing structure  270  forms a ridge  274  on both the medial and lateral sides for a sole structure. Ridge  274  is an identifiable line that defines a lasting surface, thereby defining the portions of sole structure  120  to which upper  110  should be secured. Accordingly, an adhesive, for example, may be placed between the portions of ridge  274  that are located on the medial and lateral sides in order to properly secure upper  110  to the lasting surface of sole structure  120 . 
     Reinforcing structure  270  may further include a chamfered surface  276 . 
     Chamfered surface  276  may face outwardly towards medial side  208  and lateral side  210  to provide a smoothly transitioning surface between chamber  200  and reinforcing structure  270  once chamber has been inflated. Once molding is complete, chamber  200  may be inflated with fluid. As shown in the example of  FIG. 9B , the sidewalls of chamber  200  may bulge outward towards medial side  208  and lateral side  210  when chamber  200  is inflated. However, the curvature of chamfered surface  276  of reinforcing structure  270  may provide a relatively smooth transition between the sides of chamber  200  and reinforcing structure  270 , as shown in  FIG. 9B . 
     Manufacturing Process 
     Turning to  FIGS. 10A-10D , an exemplary process is shown for producing chamber  200 . As shown in  FIG. 10A , a mold  400  may be provided, which includes an upper half  420  and a lower half  410 . Upper half  420  and lower half  410  combine to form an internal cavity having a general shape corresponding with chamber  200 . As an initial step in the process of forming chamber  200 , reinforcement member  270  may be located within mold  400  so that reinforcement member  270  is molded, bonded, or otherwise secured to chamber  200  during later stages of the molding process. As shown in the example of  FIG. 10B , reinforcement member  270  may be placed within one of the mold halves, such as upper half  420  and in a portion of the cavity corresponding with the location of  270  in chamber  200 . Subsequently, a first sheet  500  and a second sheet  510  may be placed within mold  400 , as shown in  FIG. 10C . First sheet  500  and second sheet  510  may be provided as lower and upper barrier layers for a bladder and may be made from the materials described above for barrier layers. More particularly, sheets  500  and  510  respectively form barrier layers  292  and  294  in chamber  200   
     Lower half  410  may include projections  412  while upper half  420  includes indentations  422  corresponding with projections  412 . Projections  412  and indentations  422  correspond with indentations  240  of chamber  200 . As a result, when upper mold  420  and lower mold  410  are closed together, as shown in  FIG. 10D , first sheet  500  and second sheet  510  are heated and conform to the shape of the surfaces of upper mold  420  and lower mold  410 , with first sheet  500  and second sheet  510  being bonded in the areas of indentations  422  and projections  412  to form structures in chamber  200 , such as internal bonds  230  and indentations  240  of chamber  200 . Other projections and indentations may be included to provide other bonded areas of bladder, such as the internal bonds described above. 
       FIG. 10E  shows an exemplary molded product  600  produced by a process similar to that described above. Molded product  600  may include an outer bonded portion  602  which has been produced by first sheet  500  and second sheet  510  being pressed and bonded between mold halves. A central portion of molded product  600  may include the structure of chamber  200 . For example, the molded product  600  may include a peripheral subchamber  624  and subchambers  620  in heel, midfoot, and forefoot regions. A conduit  610  is provided in the molded product  600  so that pressurized fluid may be introduced during the molding process to inflate the molded product  600 , with the conduit  610  being subsequently closed to provide sealed conduit  250  and seal the fluid within unbonded areas of the molded product  600 . Molded product  600  may include indentations  650  extending through bonded portion  602  and into the central area of molded product  600  to form indentations  240  discussed above. Indentations  650  may correspond to and be formed by the indentations  422  and projections  412  of mold halves  410 ,  420  discussed above, so that when mold halves  410 ,  420  close together, indentations  240  are formed between indentations  422  and projections  412 . 
     Further Configurations 
     As shown in the example of  FIG. 11 , a chamber  700  may be provided that does not include a peripheral subchamber. Chamber  700  may include inflated areas  720  and bonded areas  702 . Bonded areas  702  may separate inflated areas  720  from one another and may continuously extend across chamber  700  from a medial side  740  to a lateral side  742 , as shown in  FIG. 11 . Further, bonded areas  702  may have a substantially continuous shape in a direction extending between medial side  740  and lateral side  742 , as shown in  FIG. 11 , or may have varying shapes as shown in  FIG. 4 . Inflated areas  720  may be provided in the form of tubes or other shapes and may vary in number and size, as discussed herein. 
     A chamber may include separate inflated portions. As shown in  FIG. 12 , a chamber  800  may include a first inflated region  810  and a second inflated region  812  separated by a bonded area  850 . Bonded area  850  may completely seal upper and lower barrier layers of bladder  800  so that first inflated region  810  and second inflated region  812  are not fluidically connected, or first inflated region  810  and second inflated region  812  may be fluidically connected. First inflated region  810  and second inflated region  812  may each include a peripheral chamber  824  and subchambers  820  and internal bonds  830 . 
     In some configurations, only a portion of a chamber may include inflated portions. As shown in  FIG. 13 , a first region of a chamber  900  may include subchambers  920  enclosing a pressurized fluid and having internal bonds  930  while a second region is provided by a bonded area  910 . The first region of chamber  900  may be provided in a midfoot region  932  and/or forefoot region  930 , while bonded area  920  may be provided in a heel region  934  and may also extend into midfoot region  932 . In another configuration, a chamber  1000  may include a bonded region  1010  in a forefoot region  1030 , which may also extend into a midfoot region  1032 , as shown in  FIG. 14 , while a heel region  1034  includes an inflated portion with internal bonds  1030  and subchambers  1020 . According to another example, inflated portion in heel region  1034  may also extend into midfoot region  1032  in  FIG. 14 . 
     Instead of providing subchambers in pairs on a bottom surface of a chamber, as shown in  FIG. 5 , subchambers may be individually separated on the bottom surface by bonds running laterally from one edge to another. Turning to  FIG. 15 , which depicts a bottom view of a chamber, subchambers  1120  and internal bonds  1130  and a bonded area  1110  may be similar to those discussed above. However, subchambers  1120  may be separated from one another by bonds  1130  that laterally extend between an edge on medial side  1140  and an edge on lateral side  1142 . As shown in the example of  FIG. 15 , bonds  1130  may have a substantially uniform or continuous shape from medial side  1140  to lateral side  1142 , or bonds  1130  may have a shape with laterally extending portions as shown in  FIG. 5 . Although subchambers  1120  in the heel region are not individually separated by bonds in  FIG. 15 , subchambers  1120  in the heel region may also be individually separated by bonds  1130 . 
       FIG. 16  shows a side view of an article of footwear  1200 , which includes an upper  1210  and a midsole  1220  that includes the features according to any of the configurations described herein. Midsole  1220  may include flexion indentations  1222 , which may correspond to indentations  240  of chamber  200 . Footwear  1200  may also include an outsole  1230  that extends into flexion indentations  1222 , as shown in  FIG. 16 , thereby forming a stiffer, less compressible areas that also facilitate flexing about flexion indentations  1222 . Outsole  1230  may also include ground engaging members, such as lugs  1232 . As shown in the example of  FIG. 16 , lugs  1232  may be located relative to flexion indentations  1222  so that lugs  1232  are not located within flexion indentations  1222 . As a result, the location of lugs  1232  may have minimal effect upon the bending of midsole  1220  and outsole  1230  at flexion indentations  1222 . 
     Other alternative arrangements and configurations for a chamber may be provided. For example, although  FIG. 3  shows chamber  200  having subchambers  220  in heel region  202 , midfoot region  204 , and forefoot region  206 , subchambers  220  and corresponding internal bonds  230  may be located in only one of these regions, two or these regions, or one of these regions. For example, subchambers  220  may be located in only one of the heel region  202 , midfoot region  204 , and forefoot region  206  while the remainder of chamber  200  includes a large bonded area or a large area including pressurized gas. In another example, two of heel region  202 , midfoot region  204 , and forefoot region  206  may include subchambers  220  while the remainder of chamber  200  includes a large bonded area or a large area including pressurized gas. 
     As discussed above, subchambers  220  may vary in number and may vary in shape and/or size. In addition, internal bonds  230  may also vary in number, shape, and/or size. For example, chamber  200  may include subchamber  225  and subchamber  227  in forefoot region  206  of chamber  200  that do not extend between medial side  208  and lateral side  210  of chamber. Internal bonds  230  separate subchamber  225  from subchamber  227 . As shown in the example of  FIG. 4 , subchambers  225 ,  227  may be smaller than other subchambers  220  in midfoot region  204  and forefoot region  206 , with subchambers  225 ,  227  extending to a smaller extent in a direction between medial side  208  and lateral side  210  than subchambers  220 . 
     Although the example of  FIG. 5  depicts chamber  200  as including four subchamber pairs  260 , any number of subchamber pairs  260  may be utilized in chamber  200 , such as when (a) multiple chambers  200  are provided in different sizes according to the size of a wearer&#39;s foot and (b) different degrees of support or force attenuation are desired. Subchamber pairs may also vary in shape and/or size and may extend in different directions than just laterally across the width of a chamber between a medial side and lateral side. Although internal bonds and indentations  240  may extend laterally as shown in  FIG. 5 , (i.e., between medial side  208  and lateral side  210 ) across the lower surface of chamber  200 , which may be suitable for footwear structured for running and a variety of other athletic activities, internal bonds and indentations  240  may extend in a generally longitudinal direction (i.e., between forefoot region  206  and heel region  202 ) in footwear structured for athletic activities such as basketball, tennis, or cross-training. Accordingly, internal bonds and indentations  240  may extend in a variety of directions in order to provide a defined line of flexion in sole structure  120 . 
     The figures depict internal bonds  230  and indentations  240  as extending entirely across chamber  200 . In some configurations, however, internal bonds  230  and indentations  240  may extend only partially across a portion of chamber  200 . In addition, internal bonds  230  and indentations  240  may be provided in different locations than those shown in the example of  FIG. 5 . The location of indentations  240  may be selected, for example, based upon an average location of the joints between the metatarsals and the proximal phalanges of a foot. However, depending upon the specific configuration and intended use of a sole structure  120  including chamber  200 , however, the location of indentations  240  may vary. 
     According to another example, indentations  240  join upper barrier layer  292  to lower barrier layer  294  of chamber  200 , in contrast to  FIG. 6 , in which indentations  240  do not join upper barrier layer  292  to lower barrier layer  294 . 
     Subchambers may have any generally elongate structure that has a hollow interior for enclosing a portion of the fluid within chamber  200 . Although subchambers may have a circular cross-sectional shape that provides a cylindrical structure, as shown in  FIG. 7 , subchambers may also have oval, triangular, square, hexagonal, non-regular, or a variety of other cross-sectional shapes. 
     As noted above, subchambers may decrease in size and diameter in a direction extending between a heel and toe of a bladder. However, the distance between the centers of subchambers may also be affected by altering the size of internal bonds located between subchambers. 
     The invention is disclosed above and in the accompanying figures with reference to a variety of configurations. The purpose served by the disclosure, however, is to provide an example of the various features and concepts related to the invention, not to limit the scope of the invention. One skilled in the relevant art will recognize that numerous variations and modifications may be made to the configurations described above without departing from the scope of the present invention, as defined by the appended claims.