Air leakage has long been one of the most significant—and least visible—sources of energy loss in buildings. Even well-insulated assemblies can underperform when uncontrolled air movement bypasses the thermal barrier, carrying heat and moisture through gaps and discontinuities.

Uncontrolled air leakage can transport significant quantities of water vapor into wall and roof cavities, where condensation may occur. In fact, air leakage typically moves an order of magnitude more moisture than vapor diffusion, making air control the most critical component of enclosure moisture management.