HDF-Hardboard, also called high-density fiberboard, not to be confused with Hardwood, is a type of fiberboard, which is an engineered wood product. It is similar to particle board and medium-density fiberboard, but is denser and much stronger and harder because it is made out of exploded wood fibers that have been highly compressed. Consequently, the density of hardboard is 31 lbs. or more per cubic foot (500 kg/m³) and is usually about 50-65 lbs. per cubic foot (800-1040 kg/m³). It differs from particle board in that the bonding of the wood fibers requires no additional materials, although resin is often added. Unlike particle board, it will not split or crack. It is used in construction and furniture. Hardboard is produced in either a wet or dry process. The wet process leaves only one smooth side and dry processed hardboard is smooth on both sides.