The Heat Factory Great Outdoors Bonus Pack is customized to keep the outdoor adventurer comfortable in cold weather situations. Whether you need emergency warmth or just want to be prepared for that next camping, hunting or fishing trip , keep a supply of high-quality, lightweight Heat Factory warmers in the gear kit. The Heat Factory warmer is a soft, lightweight pouch containing a biodegradable mixture of iron powder, charcoal, salt, sawdust and vermiculite. When exposed to the air, an oxidation process takes place that generates heat. Heat Factory warmers are specially engineered to provide heat that is long-lasting, comfortable, and even. Heat Factory continually tests its products to ensure that you receive only the highest quality warmers that will consistently deliver warmth as advertised. Once activated, Heat Factory warmers can even be saved for later use (preferably within a week) if placed in an airtight container. Unopened, the Heat Factory warmer has a shelf life of three years or more.