Shredding is a generic term used to describe the process by which mechanical forces are used to break solid waste materials into smaller, uniform particle sizes. Usually, municipal waste has a low, but nonuniform bulk density. Size reduction increases the homogeneity, the bulk density, and the surface area to volume ratio. The increased density results in more efficiency in transporting of waste and in the need for less landfill waste. Several types of shredders that have been used for processing solid wastes are flail mills, hammer mills, grinders, shears, and wet pulpers. When municipal solid waste is processed for use as fuel, a flail mill provides the first step in primary shredding. Size separation techniques are then used to remove rocks, glass, or grit, and magnetic separation is employed to remove ferrous metals. Finally, paper, plastics, and other combustible components are shredded by a hammer mill to a smaller size.