The phrase vapor barrier is often use to refer to any material, typically a plastic or foil sheet, that resists passage of moisture through wall, ceiling and floor assemblies of buildings. Technically many of these materials are only vapor retarders as they have varying degrees of impermeability. This article will use vapor barrier although increasingly vapor retarder is used in building codes. Vapor barriers resist moisture from penetrating through the barrier and the moisture will instead remain on the side the barrier originating the moisture.