Heat Factory Acrylic Blend Pocket Socks for use Foot & Toe Warmers Special pocket sewn in above the toes to hold Heat Factory Foot Warmers (Warmers sold separately) Cushioned arch, reinforced heel, above calf length 93% acrylic, 7% polyester Medium fits men's US shoe sizes 4.5 - 8, women's US shoe sizes 5 - 10.5; Large fits men's US shoe sizes 8.5 - 13, women's US shoe sizes 11 - 12 Made in USA