Air barriers are an essential component of a well-performing building envelope. They are the first line of defense in maintaining energy efficiency and improving indoor air quality. As moisture and air seep into a building, its structural integrity begins to deteriorate, resulting in poor building envelope performance. Unexpected air leakage through the building envelope carries moisture, which can promote mold and rust in the building structure, as well as cause higher energy consumption. The United States Department of Energy states that up to 40% of heating and cooling energy can be lost through this uncontrolled movement of air, driving up energy usage and cost. The best prevention is to design an airtight building envelope, consisting of properly installed, top quality air and moisture barrier materials.