Thinsulate™ insulation, polyester outer shell laminated to a brushed nylon lining with reinforced expandable nylon front seam. Conforms and wears like a sock with the warming power of thinsulate. Wear under your favourite boot for maximum warmth and comfort. Wear alone just to keep your feet comfortable. Available in men's sizes: small (5-7), medium (8-9), large (10-11), and XL (12-13).