What Material Has the Best R-Value for Metal Garage Door Panel Insulation?

Polyurethane Foam

• In terms of advertised R-value, internal polyurethane foam insulation has the highest rating. Manufacturers blow a liquid mixture into the cavity in the middle of the door's metal panels where it expands and solidifies into a rigid foam that entirely fills the cavity. The advertised R-value of this type of insulation is typically between 12 and 18, and values around 17 are common. Polyurethane is often used in high-end metal doors, and it has the advantage of also adding structural rigidity to the door.

Polystyrene Foam

• The insulating capability of internal polystyrene foam, again in terms of advertised R-value, is a close second to polyurethane foam. Polystyrene is installed in the door panel in a manner similar to that of polyurethane insulation and also forms a solid core that fills the door panel cavity. Advertised R-values for polystyrene insulated door panels typically range between 5 and 10. Polystyrene insulation is commonly used in lower-end metal doors.

Foam Panels

• Rigid polystyrene foam board insulation is an add-on solution for uninsulated metal door panels that offers insulating capability significantly better than that of fiberglass batt insulation of a comparable thickness. Foam boards come in 1/2-inch or 1-inch thicknesses; 1/2-inch boards have an R-value of between 3 and 4, and 1-inch boards have an R-value of as much as 6.5. Batt insulation, by contrast, has an R-value of 3 to 4 per inch of thickness. Installation of foam board insulation involves simply cutting the board to fit tightly in the space on the back side of the door panel and squeezing it into place.

R-Value Limitations

• Although they reflect the insulating capabilities of the material in question, advertised R-values can be misleading. Often the advertised value is determined by measuring heat loss only at the center of an insulated door panel, but heat loss at other parts of an assembled door may be much greater. Air leaks between panels and around the edges of the door will often make the average R-value of the entire door much lower than the advertised R-value of the individual panel. The R-value of the insulating material is a good place to start in determining the efficiency of a door. However, the R-value of the entire door and the air-tightness of the door installation are important considerations, too.