Firstly we can know the specifications of foot warmer
Size: 250x75mm or 230x70mm
Weight : 72g
Heating Last: 6hours,
Average Temp: 38C
Max Temp: 45C
Secondly, we can talk about its natural material, which includes Iron Powder, Water, Vermiculite, Activated Carbon and Salt.etc
Thirdly, what’ is its working theory? Grabber hand warmer ingredients like iron, activated carbon and water. Once these ingredients come into contact with the oxygen in the air, the ingredients oxidize and produce heat. The combination of ingredients has been specially formulated to ensure a constant and comforting heat for a wide variety of uses.
Most of all, you should rightly store it, that is to keep it dry, put cool place and avoid direct sunlight.