Vapor barriers for wall insulation are designed to prevent moisture from moving outside a home from within, especially during colder months. A vapor barrier installed on insulation facing the warm living space prevents water vapor from condensing within the walls and causing significant damage to the structure.
A vapor barrier or retarder is any system or material that protects wall insulation and is classified based on its ability to diffuse water vapor. It is not required on walls made of stone or materials that are not damaged by water or freezing. Used with insulated walls, vapor barriers prevent water damage and wall or ceiling staining.