(1) A membrane, coating or other material that has very low water vapor transmission rates. (2) A component within a building assembly used to limit the transmission of water vapor by diffusion. Comment: The term vapor barrier is imprecise and the term VAPOR RETARDER (see also) is generally preferred.

SPFA believes that the path to a healthful, safe, high-quality and performing SPF installation travels through the hands of a knowledgeable, trained, experienced, and ideally PCP-certified professional contractor.