Living Stingy: Insulating Your Garage Door - For CheapWith about $120 of plastic-coated polystyrene (Styrofoam) we were able to insulate the door in about two hours. The material was bought at Lowe's. We bought 8 sheets for about $13 apiece. We used seven. The foam is coated with foil on one side, and a clear plastic on the other. We used the clear plastic on the inside, as it provided an attractive, wipe-clean surface.