Harboard, also called high-density fiberboard, is a type of fiberboard, which is an engineered wood product. It is similar to particleboard 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 and is usually about 50-65 lbs. per cubic foot. It differs from particle board in that the bonding of the wood fibers requires no additional materials, although resin is often added. Unlike particleboard, it will not split or crack. It is used in construction and furniture. Hardboard is produced in either a wet or dry process, which produce a panel called S1S or S2S respectively. The wet process leaves only one smooth side, but dry processed hardboard is smooth on both sides.