Seamless Primeknit upper for a snug, sock-like fit that stretches and moves with your foot for a truly one-to-one fit. Four-way stretch heel and external butterfly heel counter work together to wrap the Achilles, lightly holding your foot in place over the footbed without restricting your natural movement. Full-length boost midsole cushioning is ultra light and ultra responsive, absorbing the force of impact and returning that energy at toe-off, propelling you to a faster, more comfortable run. TORSION SYSTEM adds lightweight stability, encouraging a smooth, more natural transition from heelstrike to toe-off. 10mm offset. StretchWeb outsole construction adapts to your unique footstrike, allowing the boost midsole particles to freely expand and contract with the natural movement of your foot. Wt. 9.4 oz.