If you're planning to buy an insulated door because you want to save energy or keep your garage warm, it's worth spending about 15 to 20 percent extra to upgrade from extruded polystyrene to polyurethane insulation. The insulating effectiveness of a garage door is its R-value. The larger the number, the better it insulates. According to Clopay, upgrading from 2-in. polystyrene to its Intellicore (polyurethane) raises the insulating value from R-9 toR-18. That's a lot of bang for the buck.