Wood flooring is a type of flooring made from the timber of hardwoods, or of spruce or hard pine. There are two basic manufactured types of hardwood. Wood flooring comes unfinished, and once installed is sanded, then finished on site. More modernly, the product is pre-finished in a factory. The products that are pre-finished are often a polyurethane finish that has added aluminium oxide, however some companies use titanium dioxide or other oxides instead. These metal oxide finishes are used in various types of floor coverings and increase the wear a hardwood floor can handle.