The Heat Factory warmer is a soft, lightweight pouch containing a mixture of iron powder, charcoal, salt, sawdust, and vermiculite. When exposed to air, an oxidation process occurs, generating heat up to 130 degrees for over 8 hours. (Bring a sturdy zip-lock bag to stop the process and use it later.) The contents are biodegradable. Unopened, Heat Factory warmers have a shelf life of three years. Place the warmers in mesh pockets near the lens and battery, ideally. Put them in our camera cases to keep things warm when not in use. Also keep your hands and feet warm. (Includes 24 heat packs)nnFeaturesnn- Customisable solutionn- Durable 1000 denier Corduran- Designed for professionalsn- Lightweightn- Superior performance through design simplicity