Damp proofing is defined by the American Society for Testing and Materials (ASTM) as a material that resists the passage of water with no hydrostatic pressure.[1] Waterproof is defined by the ASTM as a treatment that resists the passage of water under pressure.[1] Generally, damp proofing keeps moisture out of a building, where vapor barriers keep interior moisture from getting into walls. Moisture resistance is not necessarily absolute; it is usually defined by a specific test method, limits, and engineering tolerances.