Mountain Lab heated socks provide warmth on demand, right where you need it. A low-profile heating element completely encirclesthe toes and forefoot area. The element is powered by a lightweight battery housed at the top of the cuff, where it won’t interfere withtall boot cuffs.The socks use a 50% wool, 50% polyester blend for continuous warmth and comfort, even in damp conditions or when the socks arenot powered on. Left and right markings on the socks help with easy identification.