Waterproof Breathable Membrane boostTM' Midsole - Energy-returning properties keep every step charged with an endless supply of light, fast energy. techfitTM Upper - Delivers natural, flexible support that adheres to the contours of the foot with a sock-like fit. Lightweight, Breathable Mesh - Allows air to fully permeate the shoe's interior, thereby promoting an environment that is cooler, drier and altogether more pleasant. Welded Overlays - Support and reinforce the shoe's construction without adding undue weight. TORSIONÂ® SYSTEM - Provides substantial energy return in the forefoot and torsional stability throughout the midfoot, preventing the shoe from warping and twisting to facilitate a more stable, focussed performance.