Some chemical hand warmer ingredients include cellulose, iron, water, activated carbon vermiculite, salt, charcoal and lighter fuel. There are different kinds of chemical hand warmers, and ingredients vary depending on which chemical reaction is used to create heat.
One type of chemical hand warmer is called an air-activated iron chemical hand warmer. This type of hand warmer uses cellulose, iron, water, activated carbon, vermiculite and salt to produce heat via an exothermic, or heat-producing, reaction that occurs when iron is exposed to air.
Another type of hand warmer is the supersaturated solution type. This kind of hand warmer uses the exothermic crystallization of supersaturated solutions, such as sodium acetate, to create heat. These hand warmers also contain a small flexible metal disc that is used to initiate the crystallization. These hand warmers can be recharged by immersion in hot water. This process re-dissolves the sodium acetate in the solution, storing energy in the chemical structure of the solution.
Some hand warmers use petroleum naphtha (lighter fuel) and platinum. Like the air-activated hand warmer, this type also generates heat via an exothermic oxidation reaction between its ingredients.
A final type of chemical hand warmer uses charcoal to produce heat. These hand warmers are activated by lighting a stick of charcoal and immediately putting it out, which creates an ember. This chemical hand warmer usually contains metal or another material that does not burn, in order to distribute the heat evenly. They are also covered with felt so that the heat from the burning charcoal does not become too intense for the user.