Faced insulation typically refers to insulation materials that have a vapor barrier or facing attached to one side. The facing is usually made of a plastic film, such as polyethylene. The purpose of the facing is to act as a vapor retarder, preventing the movement of moisture through the insulation.
Whether faced insulation needs plastic depends on the specific application and the desired performance of the insulation system. In some cases, a vapor barrier or facing may be necessary to control moisture diffusion and prevent condensation within the wall or ceiling assembly. This is particularly important in climates with high humidity or temperature differentials.
However, not all types of insulation require a facing or vapor barrier. Unfaced insulation, which lacks the attached plastic film, is commonly used in areas where moisture control is not a concern, such as in interior walls or attic spaces.
It's important to consult local building codes and regulations, as well as consider the specific requirements of your project, to determine whether faced insulation with a plastic vapor barrier is necessary. Professional advice from architects, builders, or insulation experts can also help you make the right decision based on your specific circumstances.