Heat Factory Merino Wool Pocket Socks for use with Heat Factory Foot and Toe Warmers Above-calf length Merino wool sock provides protection and long-lasting warmth to your feet and legs in cold outdoor activities Integrated pockets over the toes hold heat warmers; includes two Heat Factory foot warmers that last up to six hours each Medium fits men's US shoe sizes 5-8, women's US shoe sizes 5-10; Large fits men's US shoe sizes 9-13, women's US shoe sizes 11-12 Merino Wool Blend: 71% acrylic, 12% Merino Wool, 15% nylon, 1% rubber, and 1% Other Fiber