BAREFOOT TRAINING. UPPER: Keeping the boot strong and light are Flywire supports – high strength threads that work like cables on a suspension bridge with support engineered precisely where the foot needs it while boxing. A lockdown strap has been placed in the forefoot area to account for the tremendous torque applied while punching. Because of the support structure, most of the upper is constructed with a ventilating and moisture managing mesh. MIDSOLE: The midsole is constructed with strong lightweight materials to maximize speed and stability in the ring. OUTSOLE: The outsoles of Nike Free shoes feature siping (deep slices) and reverse flex grooves to encourage flexion and extension in both directions. With a lightweight, seamless upper atop the flexible outsole, Nike Free shoes merge the natural, healthy motion of a bare foot with the protection of traditional footwear.