The best hand warmers, however, can keep them nice and toasty, whatever the weather throws at you. But there are a bewildering variety of hand warmers out there, so which is the right choice for you?

The first 'reaction' that we tried for our hand warmer involved dissolving potassium carbonate (K 2 CO 3) in water. Potassium carbonate is one of the chemicals left behind in the ashes of burnt wood.