Iron-based chemical handwarmers rely upon a simple oxidation reduction reaction to generate heat. The primary active ingredients inside the package are granules of iron, salt and water. The salt and water serve to catalyze the oxidation of iron with oxygen gas in the air forming rust. This process is exothermic, and you can really heat things up by adding a stream of pure oxygen to the handwarmer! I was able to get the warmer to heat up to 85C or roughly 185F! #chemteacherphil #chemistry | Chemt