5 Answers. Rigid foam insulation is usually a qualified vapor barrier. However, an installation between the studs can pose a challenge. To complete the vapor barrier you would want to foam-seal or tape all the sides where the rigid meets timber, because these gaps will facilitate vapor flow.Click to see full answer. Herein, is XPS foam board a vapor barrier? Extruded polystyrene (XPS) XPS comes unfaced or with a number of different plastic facings. Unfaced 1-in. -thick XPS has a perm rating of around 1, making it semipermeable. Thicker, faced XPS is stronger and can have a lower perm rating, but it is still considered a vapor retarder, not a vapor barrier.Beside above, is rigid foam insulation flammable? “Rigid polyurethane and polyisocyanurate foams will, when ignited, burn rapidly and produce intense heat, dense smoke and gases which are irritating, flammable and/or toxic. Therefore, foam can be particularly hazardous during construction or renovation, as it is often exposed. Also Know, can I use rigid foam insulation in walls? Rigid foam board insulation can be used throughout the home, but most often it is found in basement walls. After that, thin furring strips are installed on top of the foam to provide a firm base for the drywall screws and drywall.Does foam board insulation need to be covered?Rigid foam insulation, whether it is expanded or extruded polystyrene, does have to be covered if it is installed in the interior of a building. This wall covering must have a minimum fire rating to protect the insulation from quick combustion during a fire.