It is a disposable, portable heater.
Wherever and whenever, it warms up your body and maintain the stable warmth for hours. You will get comfortable heat once you open a outer bag and take out a warmer; which gets activated by air.
Each product is designed for comfortable use according to the product usage. The key factor is amount of air flowing into a warmer.
e.g. When you use a toe warmer inside of your shoe, the amount of air will be limitted. Our toe warmer is designed to generate right amount of heat even it can't get much air. Or, when you use a hand warmer inside of your pocket and you hold it by your hand or sometimes take it out, it shouldn't be too hot. Then a hand warmer is designed to generate moderate heat with much air.
The heat is generated by an oxidation reaction of iron powder with the help of activated carbon and salty water. The result of the reaction is Fe + 3/4 O2 + 3/2 H2O = Fe(OH)3 + 96 Kcal/Mol
Is it environmentally friendly?
Yes. Raw materials for the heating element are iron powder, water, charcoal, and salt, and all are environmentally friendly natural elements. They do not pollute the environment in anyway.
*However, please note that salt may change soil characteristics so that scattering of heating element is NOT recommendable.