When the internal metal strip is bent, tiny bits of metal are released, which offer ‘nucleation sites’ for crystals to form. As the crystals spread, the stored heat energy of the solution is released, heating the hand warmer up to 54°C – an exothermic reaction. 4. Do not try to use or renew it if there is a leak.


Place the wrapped handwarmer in the pot. Fill the pot with water and heat it on the stove. 3. Boil the handwarmer in the pot of water for several minutes. This will begin to reverse the chemical reaction that crystallized the sodium acetate. 2. The solution crystallises readily. Keep the water at a simmer or a gentle boil and remove the hand warmer once it is recharged. Boil until the sodium acetate has turned back into a liquid. Check the hand warmer for weak spots and leaks regularly.