Special pocket sewn in above the toes to hold Heat Factory Mini-Warmers (Warmers sold separately) * Non-slip gripper bubbles on the sole * 85% acrylic, 15% Nylon * Small fits children"s US shoe sizes 1 - 5; Medium fits women"s US shoe sizes 5 - 10.5 and men"s US shoe sizes 5 - 8.5; Large fits women"s US shoe sizes 11 -12 and men"s US shoe sizes 9 - 13 * Includes one pair of Heat Factory warmers. Warmers last up to 10 hours each