Which material is classified as a vapor barrier?

A material is classified as a vapor barrier if it has a vapor permanence of 0.1 perm or less. This low permeance means that the material significantly restricts the passage of water vapor, effectively minimizing moisture transfer between interior spaces and the environment. Vapor barriers are crucial in building construction, particularly in areas where moisture control is essential to prevent issues like mold and structural damage.

High permeability materials, which allow moisture to easily pass through, would not qualify as vapor barriers. Similarly, while plastic sheeting can often serve as a vapor barrier, not all plastic sheeting automatically qualifies unless it meets the specified low permeability criteria. Finally, a material that allows all moisture to pass through is the opposite of a vapor barrier and would actually encourage moisture movement rather than restrict it. Therefore, it is clear that a vapor barrier is specifically characterized by its low vapor permanence of 0.1 perm or less.