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Medium-density fibreboard (MDF) is an engineered wood product formed by breaking down hardwood or softwood residuals into wood fibres, often in a defibrator, combining it with wax and a resin binder, and forming panels by applying high temperature and pressure. MDF is generally denser than plywood. It is made up of separated fibres, but can be used as a building material similar in application to plywood. It is stronger and much denser than particle board.

The name derives from the distinction in densities of fibreboard. Large-scale production of MDF began in the 1980s, in both North America and Europe.

Physical properties
Over time, the word "MDF" has become a generic name for any dry process fiber board. MDF density is typically between 500 kg/m3 (31 lbs/ft3) and 1000 kg/m3 (62 lbs/ft3). The range of density and classification as Light or Standard or High density board is a misnomer and confusing. Density of board when evaluated in relation to density of the fiber that goes into making of the panel is important. A thick MDF panel at 700-720 density in case of softwood fiber panels may be considered as high density whereas a panel of same density when made of hard wood fibers is not so. The evolution of various types of different MDF was driven by the differing needs of specific applications.

Comparison to natural woods
MDF does not contain knots or rings, making it more uniform than natural woods during cutting and in service. However, MDF is not entirely isotropic, since the fibres are pressed tightly together through the sheet. Like natural wood, MDF may split when woodscrews are installed without pilot holes, and MDF may be glued, doweled or laminated, but smooth-shank nails do not hold well. Typical fasteners are T-nuts and pan-head machine screws. Fine-pitch screws do not hold well in MDF and screw retention in the edge is particularly poor. Special screws are available with a coarse thread pitch but sheet-metal screws also work well. Typical MDF has a hard, flat, smooth surface that makes it ideal for veneering, as there is no underlying grain to telegraph through the thin veneer as with plywood. A so-called "Premium" MDF is available that features more uniform density throughout the thickness of the panel.

Safety concerns
When MDF is cut a large quantity of dust particles are released into the air. It is important that a respirator be worn and the material be cut in a controlled and ventilated environment. It is a good practice to seal the exposed edges to limit the emissions from the binders contained in this material.

Formaldehyde resins are commonly used to bind the fibers in MDF together, and testing has consistently revealed that MDF products emit free formaldehyde and other volatile organic compounds that pose health risks at concentrations considered unsafe, for at least several months after manufacture. Urea-formaldehyde is always being slowly released from the edges and surface of MDF. When painting, it is a good idea to coat all sides of the finished piece in order to seal in the free formaldehyde. Wax and oil finishes may be used as finishes but they are less effective at sealing in the free formaldehyde.

Whether these constant emissions of formaldehyde reach harmful levels in real-world environments is not yet fully determined. The primary concern is for the industries using formaldehyde. As far back as 1987 the U.S. EPA classified it as a "probable human carcinogen" and after more studies the WHO International Agency for Research on Cancer (IARC), in 1995, also classified it as a "probable human carcinogen". Further information and evaluation of all known data led the IARC to reclassify formaldehyde as a "known human carcinogen" associated with nasal sinus cancer and nasopharyngeal cancer, and possibly with leukaemia in June 2004.

Veneered MDF
Veneered MDF gives dual advantage of eco friendly MDF with a decorative veneer top. In modern construction, spurred by the spiralling costs of hardwoods, manufacturers have been engineering new and better ways to achieve a high quality finishing wrap covering over a standard MDF board. This is known as a Wood veneer. The most common type of Veneered MDF is made by using Oak. This is a highly complex procedure which involved taking an extremely thin slice of hardwood (approx 1-2mm thick) and then through high pressure and stretching methods they are wrapped around the profiled MDF boards. This is only possible with very simple profiles because otherwise when the thin wood layer has dried out, it will break at the point of bends and angles.

Reference Sources

 * ASTM D5651 - 95a(2008) Standard Test Method for Surface Bond Strength of Wood-Base Fiber and Particle Panel Materials
 * Lignocellulosic Composites
 * Medium Density Fibreboard by Design Technology Department
 * Spence, William P. (2005). The Home Carpenters & Woodworker's Repair Manual. New York: Sterling. ISBN 1-4027-1055-0