Question: Is FOAMULAR® insulation a vapor barrier?
Charles writes again from Eliot, Maine: "Is foamular not considered to be a vapor barrier?"
Answer: In order to qualify as a residential vapor retarder a product must have a water vapor perm rating of 1.0 or lower (the lower the number the stronger the vapor retarder). Owens Corning FOAMULAR extruded polystyrene insulation is rated at 1.1 perm. (This is tested at one inch of thickness.)
