Sanding sheets and rolls are used for general applications such as surface preparation, deburring, cleaning, finishing, and polishing. Sheets can be backed with fiber resin, cloth, paper, or film. Fiber resin- and cloth-backed sheets are more durable for heavy-duty use, while paper-backed sheets are more flexible and economical. Film-backed sheets are best for fine finishing work. Waterproof backings are available for wet sanding. Sanding sheets can have a closed, semi-open, or open coat type. Closed coat sheets have 100% of their backing covered in abrasive grains. They are the most aggressive but produce finer finishes. A semi-open coated sheet will have about 70% grain coverage, while open coat is usually around 50% coverage. These coat types cut less aggressively but also produce a coarser finish because of the grain gaps. Common abrasive materials include aluminum oxide, ceramic, silicon carbide, talc, and diamond. Sheet grades vary from very coarse to ultrafine grade, with corresponding grit numbers. Sanding rolls are a continuous length of abrasive sanding sheets that can be cut to custom sizes.