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Medium-density fiberboard (MDF) is a type of pressed wood that is made up of small pieces of wood particles (usually softwoods) bonded together with a synthetic resin. The particles used to make MDF are much finer than those used in particleboard, resulting in a dense product with a smooth surface that readily accepts paint. The particles are steam-heated to break them down into fibers, which are then dried to reduce the moisture content. Once dry, the fibers are blended with resin and any other additives, then pressed and extruded.

MDF is widely used in drawers, cabinets, shelving, moulding and doors. It may be covered with a wood veneer in applications where a solid wood appearance is desired.

Because MDF is made almost entirely of recycled materials, it is often marketed as an eco-friendly wood option. However, the resins used to glue the wood particles together may not be eco-friendly nor safe. The most common resins are all urea-formaldehydes (UF). Rates of emissions for UF resins are much higher than those for phenol-formaldehyde (PF) resins. MDF contains the highest resin-to-wood ratio than any other pressed wood, including particleboard, and is generally recognized as being the highest formaldehyde-emitting pressed wood product. Because the wood fibers used to make MDF are so fine, a large amount of hazardous dust particles are released when MDF is cut.

Safer resins and more eco-friendly fiber options are increasingly being used by manufacturers, including straw and post-consumer paper fibers and natural soy and lignin resins. Newer types of MDF, such as E0, utilize safer polyurethane-based resins, which have much lower formaldehyde-emissions rates. Types E1 and E2 have higher formaldehyde-emissions rates than type E0, with type E2 having a higher rate than type E1.

For more information, see the UMN Publication "Indoor Air Pollution: An Evaluation of Three Agents", the Global Health & Safety Initiative Fact Sheet: Alternative Resin Binders for Particleboard, MDF & Wheatboard, and Green Seal's Choose Green Report: "Particleboard and Medium-Density Fiberboard".

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