J.B. Expedition Thermal Backpacker Outdoor Sock (2 Pairs) Content- 50% Acrylic, 22% Merino Wool, 18% Hollofil, 10% Nylon Double Cuff, Impact Support Zones (strategically reinforced zones), and Contoured Full Cushion for superior comfort and protection Merino Wool is the highest quality wool available. Superwash treatment makes it machine washable and dryable. Merino fibers provide exceptional softness and natural temperature controlmaking it the most versatile natural fiber. ProtecGuard Anti-microbial socks inhibit the growth of bacteria Hollofil is DuPonts engineered yarn that minimizes loss of heat, without creating bulk