SockGuy Wool Crew 6in Colorado MTN Cycling/Running Socks 75% IsoWool(50% Merino wool, 50% Polypropylene), 15% nylon, 10% spandex 75% IsoWool has five times the strength and durability of Merina wool alone Shrink-resistant and itch-free Stretch to fit, 2 size system Cool weather or warm weather