Rigid Foam as an Insulation Strategy Rigid foam sheathing is a form of insulation — continuous insulation, to be exact — that’s applied to the exterior of the building. Rigid insulation provides thermal protection and it can also serve as an air and moisture barrier.Click to see full answer. Considering this, is rigid insulation a vapor barrier?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. what is a rigid air barrier? Rigid air barrier systems use a solid substrate, combined with a tape system to block air flow and prevent air pressure and water infiltrating the building from the outside. Thereof, is foam board an air barrier? My understanding is that rigid EPS foam board is an open cell product. Unless the EPS foam board you use is qualified by the manufacturer as being an air barrier, you must install an air barrier in addition to the EPS foam currently being used.Is Tyvek considered an air barrier? Staple-up WRBs are not the best air barriers “It is well known that staple-up housewraps like Tyvek don’t make the best air barriers,” he says. “At least they are challenging, at best, to detail as an air barrier.