Definition of MDF (Medium-Density Fiberboard)

Medium-density fiberboard (MDF)
Medium-density fiberboard (MDF). Jeff Beneke

Definition

Medium-density fiberboard, or MDF, is a manufactured (engineered) wood product composed of wood fibers that are mixed with resin and wax and pressed into flat panels under high temperature and pressure. It is used much like plywood as a building material in residential and commercial construction. Unlike particleboard, with which it is sometimes confused, MDF cuts well and has a smooth surface that is ideal for painting. (Particleboard, by contrast, makes use of ordinary sawdust rather than fibrous wood, and as a result is less water resistant and offers less structural strength that MDF. )

MDF is a very dense product ​and, therefore, is considerably heavier than plywood or dimension lumber. Keep this in mind when building with it. Other than this slight drawback, MDF is an excellent building material, as it accepts glue bonds very well and joins securely with nails and screws with minimal chances of fracturing. 

It is best to cut MDF outdoors, as it creates a lot of dust. It is also smart to wear a respirator when cutting or sanding MDF, to avoid expose to fine dusts and to the resins used in manufacture. When exposed to moisture, unfinished MDF can swell and lose strength, so in applications where moisture expose is a possibility, exterior-grade plywoods are a better choice. 

Because MDF accepts paint so well, it is often used in visible applications, such as in cabinet carcasses that will be painted. Particleboard, on the other hand, does not accept paint very well, and so is more commonly used in hidden locations, such as for underlayment for carpeting or other flooring. 

Alternate spellings: medium density fibreboard.