Knauf Water Resistant Gypsum Backing Boards are ASTM C1396 compliant gypsum boards, specifically designed for use in areas with humidity and exposure to moisture. Field of Application: Knauf Water Resistant Gypsum Boards (GB-WR) are high performance gypsum boards used as the cladding component of drywall constructions in humid areas such as: Partition or Ceilings of Kitchens / Bathrooms Wall Linings / Furrings in Kitchens / Bathrooms Partitions with tiled finish requirements Any internal area which is exposed to humidity.