This crawl space has been wrapped with a 20-mil CleanSpace liner, a heavy-duty vapor barrier designed to help protect the space from outside interference such as air, moisture, and small pests and critters. This vapor barrier is actively blocking the Earth's moisture from rising into the crawl space, which will help keep the relative humidity down. CleanSpace is a 7-layer Polyethylene liner, much like a pool liner, with an antimicrobial called UltraFresh built into the material. This helps to keep mold and mildew growth from forming on the vapor barrier itself.