3M Softback Sanding Sponge. Superfine (500/600 grit). Flexible foam backing adapts to unique contours and can access hard-to-reach areas. Coated with a long-lasting aluminum oxide abrasive, which offers a fast cut. Waterproof bonding system allows for either wet or dry sanding applications. Sponges are made for hand sanding and work on many surface materials, including wood, metal, fiberglass, plastic, gel coats and marine paints. Great for jobs that require precision and detail. Especially useful to help eliminate finger marks. Each sponge measures 4-1/2" x 5-1/2". Sold by the box of 20.