Altra Men's 3 Sum 1.5 Running Shoe 100% Textile and Synthetic Imported Rubber sole Turn up the heat as you leave the pack behind in the 3-Sum 1.5 racing flat from Altra Zero Drop&trade;! 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. A natural running shoe with a zero-drop differential that is designed for the neutral runner looking for a barefoot-inspired feel without sacrificing cushioning. Ideal for triathlons, running, road racing and speed work. Lightweight, quick-drying air mesh upper. Asymmetrical lacing for a better fit and feel. Tongue and heel loops for quick-and-easy entry and exit. Contoured heel cup for added comfort. Seamless, sock-free design with antimicrobial lining. Removable 5 mm insole for light underfoot cushioning. Natural Ride System (NRS) features a natural shape with a zero toe-to-heel drop, and allows for a more natural ride. Dual-layer midsole is made up of EVA and A-Bound&trade; material. Zero Drop&trade; Pla