EXCEPTIONAL NATURAL FLEXIBILITYMore flexible than the 5.0 and more cushioned than the 3.0, the Nike Free 4.0 Flyknit Women's Running Shoe unleashes your natural stride with a lightweight, supportive Flyknit upper and highly flexible, low-profile outsole.Ultralight SupportThe Flyknit upper—a one-piece layer made entirely of polyester yarn—seamlessly integrates areas of stretch and structure, providing ultralight support and a contoured fit. Knit-in Flywire cables cradle the midfoot for enhanced support where you need it most.Exceptional FlexibilityNew hexagonal flex grooves are hot-knife cut into the outsole, wrapping around the sidewall so your foot moves more naturally in every direction. Secondary cuts intersect the flex grooves for even greater flexibility.Natural StrideThe heel mimics the shape of the foot to promote a more natural footstrike.6mm OffsetWith a 6mm difference between heel and forefoot height, the Nike Free 4.0 Flyknit gets you closer to the ground for a more natural feel while still offering a great blend of cushioning and support.More BenefitsAttached Nike Flyknit tongue with notches for easy entryMinimal sockliner molds to your foot's curvature for added support and comfortNon-stretch, knit-in heel for structure and supportAsymmetrical lacing for reduced lace pressure on the top of your footWaffle outsole lugs help absorb impact and add responsivenessWeight: 6.6 ounces (women's size 8)Nike Free OriginsAfter learning that Stanford athletes had been training barefoot on the university's golf course, three of Nike's most innovative and creative employees set out to develop a shoe that felt natural and weightless, similar to bare feet. In 2002, they examined a group of men and women with pressure measuring insoles taped to their feet, using high-speed cameras to capture images of each foot in motion.The team spent eight years studying the biomechanics of shoeless running. The results yielded a profound understanding of the foot's natural landing angle, pressure and toe position, allowing Nike designers to build an unconventional and flexible running shoe from the inside out. Since Nike Free's introduction, millions of runners have trained in the shoe, including some of Kenya's world-class runners.Flyknit OriginsNike Flyknit technology was inspired by feedback from runners craving a shoe with the snug (and virtually unnoticed) fit of a sock. Nike embarked on a four-year mission with teams of programmers, engineers and designers to create the technology needed to make the knit upper with static properties for structure and durability. Then the precise placement of support, flexibility and breathability-all in one layer-was refined. The result is a featherweight, form-fitting and virtually seamless upper.