Wrightsock Women's Running Ii Lo 3 Pack Athletic Socks Inner: 70% Polyester, 30% Nylon; Outer: 71% Polyester, 24% Nylon, 5% Lycra Machine Wash Double layer construction coupled with the most technically advanced fibers, delivers the blister protection that you need, guaranteed The outer layer is constructed of performance fibers specific to each activity, the interaction between layers absorbs friction which prevents blisters Two layers trap air for effective insulation from heat and cold Inner layer is smooth, undyed, hydrophobic dri-wright wicks moisture away for cool, dry feet Patented 3rd attachment keeps socks properly aligned