The gloves use a heating system called Aevex that maintains an even temperature without a bulky, power-hungry thermostat. When your hands get cold, so does a thin polymer film in the gloves. This changes the density of the film, increasing its electrical conductivity so that it starts to pull power from a battery in the wrist. As your hands warm up to their usual temperature, they stop drawing heat from the film and instead start transferring heat to it. That reduces conductivity, shuts off the current flow, and saves battery life.