5" Hook Velcro Wet/Dry Film Sanding Discs, 50-Pack Special waterproof polyester film aluminum oxide (A/O) loop backed (velcro) hook and loop plastic film discs are a solid choice for wet finishing on automotive or other applications needing waterproof abrasives. These polyester discs are precisely stamped and bonded with an industrial grade hook and loop (velcro hook) backing. Film material provides a high strength product and a solid finish with a long working life. These discs work great on metal working applications. Use in wet or dry applications.