We have available to us one of the greatest insulating materials ever designed at NASA. In space, astronauts have to withstand temperatures of -200 to a +200. For this reason NASA applied "Heat Mirror" technology, or the ability to trap and reflect radiant heat into the construction of their suits. Conductive heat loss is the primary reason for you turning cold, or in the reverse for something staying cold. Heat is always moving towards the cold. That is why NASA technology used in Hot Feet traps your body heat.