Vapor Retarders are intended to prevent the transmission of water vapor. These are required by code to be placed on the warm-in-winter side of the wall. These include polyethylene sheets, asphalt-backed kraft paper commonly used as insulation facing, foil laminate faced insulation and interior paints. These locate within the wall section continually prevent vapor transmission. These can minimize the deleterious effects of moisture in wall cavities. These are also used as ground covers for basements or crawlspaces.