What is MDF: A De-Mystification of Medium Density Fiberboard (MDF)

You’ve probably heard of a building material referred to as “MDF,” and you may have a vague idea of what it is…but that’s where it ends. In this article, we’re going to look at what MDF is, how it’s made, and some of the pros and cons of using it.

Definition of MDF:Technically, medium density fiberboard (MDF) is a high-grade composite material that is somewhat similar to wood. Casually, however, MDF has also become a generic term to mean any dry-process fiberboard (Wikipedia).

How MDF is Made:MDF is an engineer lumber made from wax, resin, andrecycled/mashed wood fibers．Those materials are machine-dried with high heat and high pressure methods, and when hardened, the pulpy mix is pressed into dense, flat, stable (e.g., not knotty) sheets of MDF. The wax in MDF gives it moisture resistant properties, and the resin keeps the mixture of materials uniform and dense.

MDF, when completed, is a composite somewhat similar to particleboard (think: Ikea furniture), although MDF is significantly more dense, strong, and stable. For these reasons, over the years, many large-scale furniture makers have implemented MDF for mass production of veneered products.

Benefits + Pros of MDF:

When compared to solid wood, MDF is more stable and isotropic, meaning that its properties are the same in all directions because there is no grain. Because natural wood has grain, knots, and/or rings, it is less uniform than MDF. Thus, MDF can be cut more precisely and avoid splitting better than wood.

MDF is better able to withstand changes in humidity and temperature (heat) than solid wood.

MDF can be easily laminated, glued, or doweled. In some circumstances and higher grades, it is relatively easy to paint/finish.

MDF can be less expensive than solid wood, depending on the variety of MDF (premium MDF is denser, and some hardwoods are more expensive than others).

In general, MDF is flat and smooth-surfaced (fibers are pressed very tightly together to comprise the material, so it’s not completely uniform, but it’s close). This hard, smooth quality makes MDF an ideal substrate for veneers because no underlying grain or inconsistencies in hardness transfers through thin veneer with MDF.

MDF is consistent in strength and size (unlike hard wood, which can expand/contract in size), and it can be cut/shaped well. This is largely due to its composite and nearly isotropic properties.

MDF is increasingly green, or environmentally friendly. Because many of its components are recycled content as well as from sustainable forests, it doesn’t put a strain on the environment as much as natural wood use can.

Disadvantages + Cons of MDF:

MDF often comes pre-primed; however, the pre-priming is generally insufficient for most finish painting, particularly with latex paints. The paints are absorbed quickly, which means finishes and paint will appear splotchy and uneven.

Although MDF is adept at withstanding changes in humidity, it is prone to swelling and breaking if saturated with water (e.g., MDF baseboards with flooding, cabinetry with water spills, etc.). This is true of all MDF but particularly low-grade MDF pieces.Conversely, MDF can shrink when used in very dry (e.g., low humidity) areas.

MDF has poor moisture resistance qualities and, thus, has a tendency to warp or expand in its raw state. It must be thoroughly sealed (front and back, top and bottom), and even then must be sealed regularly. This is why MDF is primarily used for indoor applications.

The cutting and sawing of MDF has a tendency to dull blades faster than natural woods’ cutting and sawing. This is due in large part to the extreme density of MDF; the blades are cutting through more mass per cut than during wood cuts.

MDF can be heavy. Because it’s denser than plywood or chipboard, with its heavy resins, MDF isn’t light. This can play a role in its suitability for some building applications. Conversely, however, MDF can sometimes be used in veneering applications to produce lighter-weight pieces than solid hardwood.

The surface of MDF can split when screwing into the board (although it doesn’t tend to split on the sides, like natural wood does).

(Note: The photos in this article include MDF construction as well as other materials, such as hardwood.)