Mylar Backed Sanding Film

This stuff has been around forever, but few people seem to know about it. It's like sandpaper, but the abrasives are based on a plastic film. You can roll it, fold it, and wet-sand with it without ruining the sheet or causing grit to get all over your work. I wash sheets that have become clogged or dirty in my kitchen sink. Heavy use makes the stuff more flexible and finer; I have comfortable old scraps in my toolbox that I've been using for five years. The extra-fine varieties can be used to smooth and polish plastic and certain types of paint finishes.

You'll find sanding film in craft or hobby stores; it comes in small (typically 4"x5½") sheets in a variety of grits. Several brands are available. The ones I've seen most often include Flex-I-Grit (by K&S Engineering) and Super Film (by Houston Art, Inc.).

Available at hardware stores.