The Heat Factory Hand Warmer Big Pack features 12 pairs of Heat Factory Hand Warmers. Each Hand Warmer offers up to 10 hours of quality, safe and continuous heat. 12 pair of Heat Factory air-activated handwarmers. Heat Factory warmers is a soft ,lightweight pouch containing a biodegradeable mixture of iron powder, charcoal, salt and vermiculite. When exposed to the air, an oxidation process takes place that generates heat that last up to 10 hours. Heat Factory warmers are flameless and odorless. This Big Pack is perfect for keeping in a car in case of emergency or taking along on any trip in the outdoors.