Insulating the garage door is a very effective way to reduce the energy consumption in your home. Garages, like attics, get really hot in the summer time and allow heat to escape in the winter. Because most garages are attached to the home and therefore conditioned space, their heat accumulation is transferred into the house making heating and cooling units work harder than needed.
Putting foam insulation on the hot, metal garage door will prevent that heat from transferring into the garage and into your home. In the winter months the heat will be reflected back into your home where you want it.