Vapor barrier
A moisture-blocking layer that keeps humidity out of walls and crawlspaces.
A vapor barrier is a sheet of plastic or treated material that slows moisture from passing through walls, floors, or crawlspaces. It protects insulation and framing from condensation, mold, and rot. Crawlspaces in particular benefit from a ground vapor barrier to keep soil moisture from rising into the home. A torn or missing barrier can let damaging humidity build up.