3M the choice of professionals for wet sanding between coats of varnish, lacquer, paint, and other finishes. For use on paint and varnish. 400 grit. Waterproof, flexible "A" weight backing for wet or dry finishing of plastic, fiberglass, and top coats. Made with silicon carbide, a sharp synthetic mineral that cuts fast and smooth, it can also be used to repair surface defects. Can be used with water or cutting oil to reduce clogging and extend abrasion life.