3M SOFTBACK SANDING SPONGES – 3M Softback Sanding Sponges are an innovation in coated abrasives for hand sanding applications. These sanding sponges provide flexibility and conformability to allow for sanding by hand in areas inaccessible to machine sanders. 3M Softback Sanding Sponges feature aluminum oxide mineral coated on a foam pad with a waterproof bonding system. That’s right, they can be used either wet or dry when sanding on wood, fiberglass/gelcoat, marine paints, metals and plastics. Sponge is 4-1/2″ x 5-1/2″. Product is sold by the individual sponge.