Premium feet heat warmers — warm feet for 8h+! The heat duration, temperature, and activation time of the toe heat warmer may vary depending on the oxygen content of the environment. The warmers are designed for use in shoes of all kinds. After a few minutes, the toe heat packs reach the maximum heat, and then offer a pleasant 102°F (on average) for 8 hours and more. The heated foot warmers do not have to be boiled or heated in the oven! Simply open the packaging and remove the adhesive warmer. Then, insert the toe warmers disposable with the smooth side down into the shoes and enjoy the warmth. If you do not need the full length of heat time of the hot toes warmers all at once, you can pack them airtight, and use them again later, until the bootwarmers have fully reacted. The natural ingredients of the air activated warmer are harmless to health and environment. Thus, the toe heat warmers can be disposed of after use with regular residual waste. Unopened, they keep for several years.