Chemical handwarmers are useful for backpackers, campers or anyone who spends a lot of time outdoors in the cold winter months. Handwarmers are a welcome device for thawing cold fingers and hands. Disposable handwarmers provide heat through an exothermic chemical reaction between iron powder, salt, water and activated carbon which react with oxygen in the air when the handwarmer pouch is opened. But these handwarmers are less practical because they cannot be reused. Reusable handwarmers operate on the same principle but contain a solution of sodium acetate that releases heat as it crystallises.
Wrap the used handwarmer in the cloth. This shields it from damage and overheating. Make sure the cloth covers the handwarmer completely. An old sock or bandanna will work well.
Place the wrapped handwarmer in the pot. Fill the pot with water and heat it on the stove.
Boil the handwarmer in the pot of water for several minutes. This will begin to reverse the chemical reaction that crystallised the sodium acetate. Boil until the sodium acetate has turned back into a liquid.
Remove the handwarmer from the pot and store it for later use. When you're ready to use it again, click the disk to activate it, or follow the instructions that came with the handwarmer. It should provide heat for anywhere between 30 minutes to several hours.