Karebac LR5C320 Premium Gold 5" PSA 320-Grit Sanding Discs C-Weight Aluminum Oxide Stearated (Pack of 100) Used for wood metal plastic fiberglass paint primer solid surface materials composites Open coat grain with a non-loading stearate minimizes loading with a cool cut for longer lasting abrasives Strong C-weight paper backing P graded aluminum oxide grain provides fast smooth cut while fracturing to create new cutting services extending abrasive life Full resin on resin bond adheres the grain to the cutting surface making the disc waterproof