Unleash those animal instincts and power through your next run in the lightning-quick speed One 2.5 running shoe! Altra Zero Drop recommends that those new to natural running and zero-drop footwear transition slowly by wearing these on shorter runs and gradually building up to regular mileage. Successor to the One 2. Built on a neutral last for experienced athletes looking for fast lightweight performance. Ideal for running racing speed work training and walking. Designed to improve running form toe splay natural stability and comfort. Quick-drying breathable mesh upper with thin synthetic overlays. Foot-shaped toe box allows toes to relax and move freely providing enhanced comfort natural stability and a more powerful toe-off. Slightly padded tongue and collar. Breathable textile lining supplies a great in-shoe feel. 5 mm Contour insole. Dual-layer EVA midsole features A-Bound top layer that absorbs impact and rebounds energy with each stride. InnerFlex technology adapts to foot's natural flex by employing omnidirectional flex grooves in the midsole. Fully cushioned Zero Drop technology promotes a more natural foot strike and a more efficient stride. Rubber outsole with FootPod technology. Weight of footwear is based on a single item not a pair. Proposition 65 WARNING: This product contains chemicals known to the State of California to cause cancer and birth defects or other reproductive harm.