Composite Cores are either Particleboard or Medium Density Fiberboard (MDF). There are significant differences between the two, and each offers a number of variations. Both particleboard and MDF are made from small particles of wood compressed with an adhesive to create a solid, flat panel of uniform thickness. Composite cores are valued for their flat, smooth surfaces and tight tolerances, as well as their relatively low costs. They are also heavy, can spread or shrink as much as 3%, and are not as strong as veneer cores.
Particleboard is perhaps the least expensive core for hardwood plywood because its particles are less refined than MDF, yet it is perfect for many applications. It is smoother and more uniform than veneer cores and available in Class A fire ratings as well as no-added-urea-formaldehyde constructions. Particleboard is generally available 1/2" or thicker. While some hardwood plywood producers manufacture their own particleboard, most outsource this core material.
MEDIUM DENSITY FIBERBOARD
Medium Density Fiberboard is manufactured from highly refined wood particles into an extremely dense panel that in addition to being very smooth and uniform in thickness, will machine more like solid wood than either particleboard and veneer cores. MDF is also available in Class A fire rating and NAUF. MDF is available in both thin and thick panels. As with particleboard, most hardwood plywood manufacturers outsource their MDF supply.