Glass paper, also known as sandpaper, is an abrasive paper used for smoothing rough surfaces, removing paint and eliminating rust. This material consists of a heavy paper coated with abrasive granules, such as sand or tiny glass fragments. According to About.com, popular uses for coarse glass paper include stripping paint and removing rust, while finer grades are used primarily for smoothing and polishing.
The most basic varieties of glass paper consist of an abrasive bonded to heavy paper with hide glue. Many modern glass paper manufacturers use backings made with a combination of paper and cloth. This makes the glass paper very difficult to rip and increases its suitability in high-friction applications.
Hide glue was once the only adhesive found in glass paper. It provides strong adhesion but does not tolerate moisture or high temperatures. Modern glass paper often contains resin instead of hide glue. The most common resin adhesives are urea- or phenolic-formaldehyde resins. They provide a strong bond, are nearly impervious to water and tolerate high temperatures.
According to Wikipedia, the most common abrasives found in glass paper are aluminium oxide, silicon carbide, ceramic aluminum oxide, emery and garnet. Aluminium oxide is the least expensive and most common abrasive. Glass paper made with this abrasive comes in a huge range of grit sizes.