How to Insulate Garage Doors. Adding insulation to your garage doors will help keep cold air out in winter and the heat out during the summer. While insulating your garage door won't turn your garage into a warm winter haven by itself-it will help make the temperature a little more pleasant. However, the real bonus from insulating a garage door comes in hot areas of the country where the sun beating directly onto a flat garage door can raise the temperature inside the garage 25 or 30 degrees, making it a real sauna inside and raising your home cooling costs. Here's an inexpensive way you can insulate your garage door to keep the heat outside and help make the inside temperature more livable-and save you some money on your energy bills.
Measure the height of each of your door panels and cut the 1 inch poly insulation into 2-inch-wide strips about 1 inch shorter than the height of the individual door panels.
Use industrial adhesive to glue the strips onto each door panel. Place one strip near each end of a door panel and two strips near the middle of each door panel. These will act as setbacks or block to keep the next layer, the reflective insulation, from coming in contact with the door surface.
Cut the ½-inch-thick reflective insulation into panels the same size as the garage door panels. Also cut them to fit end to end.
Position the reflective insulation panels onto the back of the door. Depending on the design of your garage door you may be able to just fit them into the sides of the doorframe. Alternatively, you can glue them directly onto the poly strips already in place.
Be sure to install the insulation with the reflective side facing towards the door (not facing into the garage). The reflective surface in combination with the air space you've created will stop that transfer from the door's surface into your garage.