There are two main types of insulation that you can install on your garage door. You’ll either have polyurethane or polystyrene. There is a difference between these two insulators. Polystyrene is thicker, but it has a lower R-Value. The R-Value determines the amount of insulation a material offers.
The other type of insulation is polyurethane. It is thinner, but is actually a better insulator than polystyrene. Garage doors that are well insulated have polyurethane inserted in between the panel. It expands to fill up the inside of the panel and then bond to the material of the door.