Heat Pack

Air activated hand warmers contain cellulose, iron, water, activated carbon, vermiculite (water reservoir) and salt and produce heat from the exothermic oxidation of iron when exposed to air. They typically emit heat for 1 to 10 hours, although the heat given off rapidly diminishes after 1–2 hours.The oxygen molecules in the air react with iron, forming rust. Salt is often added to catalyze the process.