Premium heat insoles - for 8h+ comfortably warm feet. The heat duration, temperature and activation time of the foot warmers may vary depending on the oxygen content of the environment. The heating soles are designed for use in shoes of all kinds. After a few minutes, the shoe warmers reach maximum heat and provide a comfortable 39°C on average for more than 8 hours. The foot warmers do not have to be boiled up or heated in the oven. Simply open the packaging and remove the foot heater. Then insert the thermal insoles into the shoes with the smooth side down and enjoy the warmth. If you do not need the full heat duration of the foot warmers at once, you can pack them airtight and use them again at a later time until the heating inserts are fully reacted. The natural ingredients of the activated carbon warmers for single use are harmless. Thus, the shoe warmers can be disposed of in normal residual waste after use. They are durable for several years unopened.