Smart insoles that are activated the moment you take them out of the bag. Give them a little shake and and then they are activated when the contents come in contact with the air. After a few minutes, you get comfortable warmth for up to 8 hours. The soles are placed in the shoe or boot on top of the normal sole and you will have warm feet for the next 8 hours. Heats max up to 45 ° C with an average of 37 ° C. Note: Can only be used once.