The Battery Sock from Terramar is a new and improved version of a wool blend outdoors sock. Reinforced toe heel, perfect indoors or out. Stay warm and comfortable this winter! Black: New, now using 9 volt batteries not included carried comfortably in Velcro closed pouches. Integrated battery pouch on sock 71% acrylic, 19% polyester, 10% wool Blue: D cell Batteries are comfortably carried in snap closed pouches. Batteries are not included Reinforced Toe and Heel Integrated battery operated foot warmer 45% Acrylic 19% Wool 22% Nylon 1% Elastic Rubber.