【Heat duration】Up to 10 hours of lasting warm soles with an average temperature of 102°F. No electricity, boiling or additional heating of foot warmers required 【Comfort】The ultra-thin and comfortable toe warmers are barely noticeable and fit any shoe bed - whether it's a ski boot, winter boot or an elegant ladies’ shoe 【Natural material】The sole warmers consist of iron powder, water, salt, activated carbon and vermiculite. Heated insoles are the perfect product for warm feet for children, women and men 【Easily use】 Open the packaging, and the heatable insoles will heat up by themselves after a few minutes’ contact with oxygen. Remove the film from the heating inserts and stick to the top or bottom of the socks 【When to use】The shoe warmers are ideal for outdoor activities, winter sports of all kinds, winter walks and visits to the stadium and the Christmas market. Can be kept for several years unopened WarmSpark, a leading company in air-activated warmer industry, has powerful R&D productivity on hand, feet and body warmers. We are committed to provide high cost performance products for anyone wanting safe, convenient, comfortable warmth in cold conditions.