adidas Formotion Extreme Sock 98% Nylon/ 2% Spandex Imported Nylon, Polyester, Spandex Extra Small fits youth shoe sizes 9C-1Y Small fits youth shoe sizes 13C-4Y Medium fits men's shoe size 5-8.5, women's shoe size 5-9.5 & youth shoe sizes 4Y-353 Large fits men's shoe size 9-13 and women's shoe size 10-359