The house wrap acts as both a moisture barrier and additional barrier to air penetration but, it is unique in that it also is designed as a drainage plane. When siding is installed over GreenGuard RainDrop, channels remain for water to drain away from the surface and with the water gone the surface moisture dissipates through normal drying by evaporation. In addition, GreenGuard RainDrop breathes to allow moisture vapor to escape from the wall cavity