What is one key difference between an air barrier and a vapor barrier?

The key difference highlighted in the correct answer is that air barriers are designed to control the movement of air, helping to prevent air leakage in and out of a building. This is crucial for maintaining energy efficiency, indoor air quality, and overall building performance. On the other hand, vapor barriers are specifically engineered to restrict the movement of moisture in the form of water vapor, thereby preventing condensation and moisture-related issues such as mold or structural damage.

Understanding this distinction is essential for building professionals because while both types of barriers contribute to the overall effectiveness of a building envelope, they serve different functions and are made from different materials. Effective air barrier systems enhance a structure's thermal performance and reduce energy costs, while vapor barriers protect against moisture intrusion, ensuring a healthy indoor environment.