A hand warmer can provide quick, convenient heat. Unlike many other heating products, a hand warmer does not require the use of electricity or batteries, making it completely portable and maintenance free. They are safe, non-toxic and environmentally friendly. Always be prepared with a hand warmer and foot warmer in your backpack. Warmers operate on a chemical reaction with air similar to rusting. The warmer ingredients are iron, water, cellulose, vermiculite, activated carbon and salt.

The heating process takes place in this fashion:
The iron in the pouch, when exposed to oxygen, oxidizes and therefore produces heat (aka, "Air Activated").
When iron oxidizes it produces iron oxide, more commonly referred to as rust.
The salt acts as a catalyst.
The carbon helps disperse the heat.
The vermiculite is used as an insulator for the purpose of retaining the heat and the cellulose is added as a filler.
All of these ingredients are surrounded by a polypropylene bag.
Polypropylene allows air to permeate the ingredients while holding in moisture.
Camping tip: Put a hand warmer (in a sock) in the bottom of your sleeping bag to warm it up before bedding down.