What is a thin, moisture-resistant material placed to prevent moisture passage into a building called?

The term that best describes a thin, moisture-resistant material used to prevent moisture passage into a building is a vapor barrier. Vapor barriers are specifically designed to impede the movement of moisture vapor from one side of the barrier to the other, helping to protect the structural integrity of a building and enhance energy efficiency.

These barriers are commonly employed in areas prone to high humidity or moisture, such as basements and crawl spaces, where excessive moisture can lead to mold growth, wood rot, and other moisture-related issues. By limiting the amount of water vapor that can infiltrate from the soil or exterior environments, vapor barriers play a crucial role in creating a healthy indoor environment and extending the lifespan of building materials.

In contrast, other terms like water barrier, moisture seal, and humidity shield may refer to related concepts but do not specifically denote the same function as a vapor barrier. A water barrier typically prevents liquid water from entering an area but does not necessarily address vapor. Moisture seal may suggest an application meant to seal surfaces against moisture, and a humidity shield might imply protection against humidity in a broader sense, but neither focuses specifically on vapor management in the same way as a vapor barrier does.