The Heat Factory Pocket Sock in a heavyweight Merino wool blend. The Pocket Sock has a special pocket over the toes to hold Heat Factory Foot Warmers. Simply insert a Foot Warmer packet in the pocket and enjoy 6 hours of soothing warmth. Above calf length. One pair of Heat Factory Foot Warmers included (additional wamers sold separately). Heat Factory's air activated hand warmers, body warmers, toe warmers, and heated accessories have been providing warmth and pain relief to outdoor enthusiasts for the past 30 years.