Aluminum Foil Vapor Barrier for saunas 48 inches wide X 68.8 feet long and covers 275 square feet. This roll has enough aluminum foil to cover a sauna room measuring 7′ x 7′. Polyethylene, while an excellent vapor barrier, will break down and melt in the ceiling or in the area around the heater as it does not have a high temperature rating. The aluminum foil has the required high temperature rating. It is also an extra insulator as it reflects heat back into the sauna room. An installation note: The shiny side must face inwards to the sauna; trim off the excess foil at the bottom with a trimming knife and mark the edges of all nailing studs with a grease pencil (or by creasing the foil with your fingernail). By marking all of the nailing areas (including benches), you will simplify the job of nailing on the T & G cedar lining.