In Average Cold Weather Conditions (20 to 30 degrees F), a heat pack is NOT necessary. Just slip the Boot Blankets over your regular boots after reaching your stand and while your feet are still warm. Do NOT wait until your feet cool down.
In colder conditions, place a heat pack in the toe of the Overboot before you slip it over your regular boot.
In conditions such as snow, or when you wear rubber boots or a rubber boot bottom, you will probably stay more comfortable by removing your regular boot and placing a heat pack in the toe of the Overboot and then slipping the Overboot over the foot while wearing only one or two pairs of woolen socks. (This is what David Blanton, a member of Realtree's Pro Staff, does when he hunts in Canada in temperatures of -20 to -30 degrees C.) Remember that rubber retains cold more so than does leather.
A heat pack works great in the Hanblanket® Muff when you do NOT want to wear gloves or wish only to wear a pair of light-weight gloves.