Nevercold Hand Warmers are handy extra warming bags that you can use to warm your hands or keep your phone or device batteries warm on cold, frosty winter days. Nevercold Hand Warmers are small pillow-like bags made of porous material, containing a mixture of vermiculite, iron powder, wood powder, activated carbon and salt. When the sales package surrounding the bag is opened, the mixture reacts with air, which begins to generate heat. The reaction continues on its own for 10 hours. The heat production can be interrupted by moving the bag to an oxygen-free place, e.g. in an airtight minigrip bag, so that the heater can be used again later. Features activated by air when the package is opened reaches operating temperature in about 5 minutes operating time 10 hours average temperature 53 °C two heaters in the package