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.