Housewrap (or house wrap), also known by the genericized trademark homewrap (or home wrap), generally denotes a synthetic material used to protect buildings. Housewrap functions as a weather-resistant barrier, preventing rain from getting into the wall assembly while allowing water vapor to pass to the exterior. If moisture from either direction is allowed to build up within stud or cavity walls, mold and rot can set in and fiberglass or cellulose insulation will lose its R-value due to heat-conducting moisture. House wrap may also serve as an air barrier if it is sealed carefully at seams.Housewrap is a replacement for the older asphalt-treated paper, or asphalt saturated felt. These materials are all lighter in weight and usually wider than asphalt designs, so contractors can apply the material much faster to a house shell.