Warmer produces heats to use contact with iron powder and the oxygen in the air oxidation reaction. Hemei warmers equips with stable quality, safe and reliable performance. 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.