We use Open Coat Aluminum Oxide, the most popular of all sandpaper in woodworking. This material is extremely tough and has a wedge shape for high speed penetration of tough materials without excessive shedding or fracturing of the grain. Aluminum oxide is suited particularly well for grinding high tensile strength materials such as carbon steels, alloy steels, tough bronze and hard woods. As well we use "X" weight cloth backing for superior flexibility and strength.