Warmer produces heats to use contact with iron powder and the oxygen in the air oxidation reaction. Material is made with isolate air of gelatin and microporous breathable non-woven material, it can conduct fever after tearing not-breathable material , microporous breathable technology makes the iron powder contact with air, so the temperature can be maintained for a period of time. After opened outside wrapping paper, it can generally heat itself to between 51 and 60 degrees, and its persistent fever is about 12 hours.