The RFL is the lightest sock we make for the hill but it's no lightweight. It's 100% Darn Tough. Coveted by performance skiers and riders for its minimalist construction, the RFL provides plenty of warmth and a smooth, streamlined fit. This sock just disappears when you put it on. Ideal for skiers and riders who are looking for a sock that interfaces seamlessly with their boots and allows them to feel the terrain underfoot. THERMOLITE fabric and insulation provides warmth and comfort without weight. Still made in Vermont. Guaranteed for life.