The Nike Free Flyknit+ are the result of a combined 12 year effort from teams of programmers, engineers and designers to create a shoe which feels akin to running barefoot. The Flyknit uppers act like a second skin and feel natural to wear. The team spend 8 years studying the bio mechanics of shoe-less running to get a shoe that even matches a human foot on the landing angle, pressure and direction. The revolutionary Nike Flyknit upper delivers a compressive, second-skin fit that secures your foot over the Nike Free midsole. Made entirely of polyester yarn, the one-piece upper seamlessly integrates areas of high breathability, stretch and support where you need it most. The upper, midsole and outsole work together to create a more natural ride. For ultimate flexibility, the shoe's Nike Free 5.0 midsole features flex grooves to promote natural motion and help increase stability and foot strength.