Ceramic aluminum oxide is a self-sharpening grit that is harder, tougher, and lasts longer than aluminum oxide * Cloth backing is stiffer, tougher, and thicker than a paper or film backing * Resin bond for heat and moisture resistance, and retains abrasive grains well * Closed coat for a higher-quality finish than an open-coat disc * Used with a molded rubber backing pad (sold separately)