Batt, foam board and reflective insulation are materials to insulate a metal garage door. Apply these materials to the back of the garage door for insulation from the elements as well as energy efficiency.
Effective against water and air, batt insulation is a flexible material usually made of fiberglass with a paper or foam backing. Foam board insulation panels are rigid, polystyrene panels with an aluminum or vinyl coating and are most effective against air. Reflective insulation is made of rigid rolls of cardboard and polyethylene bubbles enclosed in aluminum foil on both sides; this type of insulation is particularly effective against extreme temperatures.