The 3M Softback Sanding Sponge 02602 provides flexibility and conformability to allow for sanding by hand in areas inaccessible to machine sanders. Use this sponge wet or dry when sanding on wood, fiberglass/gel coat, marine paints, metals and plastics. 3M Softback Sanding Sponges are coated with aluminum oxide mineral. Each grade uses a range of mineral sizes. Superfine ranges from grade 500 to 600.