The RUNNING XTRA sock is a thicker Double Layer sock for people who like more cushion. The inner layer is a smooth, flat knit Coolmax® against the foot. The outer layer is also constructed of heavier Coolmax® and has cushioning along the foot for added protection. The construction of two layers of CoolMax® still allows slight movement to absorb the friction. Feet stay dry as the CoolMax® wicks the moisture away from the foot and into the outer layer for evaporation. Fabric: Inner Layer 70% CoolMax®, 30% Nylon Outer Layer 68% CoolMax®, 28%Nylon, 4% Lycra® Color: White