Take your run to a whole new level with responsive cushioning. Seamless Primeknit upper stretches with the foot for a breathable, comfortable fit. Four-way stretch heel works with the tongue and butterfly heel counter to hold you in place while offering dynamic support. Full-length boost midsole provides the best in energy return and cushioning. TORSION SYSTEM creates a smoother transition from heelstrike to midfoot stance. Stretch web outsole adapts to all surfaces and supports your foot's natural movements.