What is a vapor diffusion retarder also known as?

A vapor diffusion retarder is commonly referred to as a vapor barrier because its primary function is to impede the movement of moisture in the form of vapor through building materials. By limiting this vapor diffusion, the material helps to control humidity levels within the structure, thereby preventing condensation and moisture-related issues such as mold growth and decay of building components.

The terminology emphasizes its role in "retarding" or slowing down the transfer of water vapor, distinguishing it from other materials that may only serve as barriers against liquid water or moisture. This specificity is crucial in building science, where controlling moisture is vital for the integrity and longevity of the building. Utilizing the term "vapor barrier" aligns with standard building codes and practices, making it a widely recognized and understood reference in construction and design.