option is installed at the factory utilizing the standard fiberglass
skin. The Door frame is filled with a 2" expanded styrene plastic
block, one pound in density. This styrene has an R value of 7.8. We
also skin the inside of the Door with a 6 oz. white pebbled back
liner. The back liner has limited flammability, is USDA approved,
shatter resistant, and easy to clean. 1/2" wide by 1/8" thick weather
stripping (provided by others) can be used between door frames.