Altra Women's 3-Sum Running Shoe 100% Fabric Imported Rubber sole Seamless upper Quickdraw laces Heel and forefoot drainage ports Dual-layer AltraBound and EVA foam midsole Blown rubber metapod outsole Zero Drop platform with natural ride system designed for mid- and forefoot strikers Gender specific design Built for triathletes, the 3-Sum from altra delivers minimal weight and light cushioning for a fast, agile ride.