different resins. It was found that better strength, appearance and resin economy could be achieved by using more uniform, manufactured chips. Producers began processing solid birch, beech, alder, pine and spruce into consistent chips and flakes; these finer layers were then placed on the outside of the board, with its core composed of coarser, cheaper chips. This type of board is known as three-layer particleboard. More recently, graded-density particleboard has also evolved. It contains particles that gradually become smaller as they get closer to the surface. Manufacturing Particleboard or chipboard is manufactured by mixing particles or flakes of wood or jute-stick together with a resin and forming the mixture into a sheet. The raw material is fed into a disc chipper with between four and sixteen radially arranged blades. The chips from disk chippers are more uniform in shape and size than from other types of wood chippers. The particles are then dried, and any oversize or undersized particles are screened out. Resin is then sprayed as a fine mist onto the particles. Several types of resins are used in the procces. Amino-formaldehyde based resins are the best performing based on cost and ease of use. Urea melamine resins offer water resistance with more melamine offering higher resistance. It is typically used in external applications, with the coloured resin darkening the panel. To further enhance the panel properties, resorcinol resins can be mixed with phenolic resins, but that is more often used with marine plywood applications. Panel production involves other chemicals including wax, dyes, wetting agents and release agents, to aid processing or make the final product resistant to water, fire or insects. After the particles pass through a mist of resin sufficient to coat all surfaces, they are layered into a continuous carpet. This 'carpet' is then separated into discrete, rectangular 'blankets' which will be compacted in a cold press. A scale weighs the flakes, and they are distributed by rotating rakes. In graded-density particleboard, the flakes are spread by an air jet that throws finer particles further than coarse ones. Two such jets, reversed, allow the particles to build up from fine to coarse and back to fine. The formed sheets are cold-compressed to reduce thickness and make them easier to transport. Later, they are compressed again, under pressures between and temperatures between to set and harden the glue. The entire process is controlled to ensure the correct