What is MDF?

Medium-density fibreboard (MDF) is a man-made, wood-based, sheet material which has a huge range of applications in construction, furniture-making and interior design.

A brief history of MDF 

What is MDF used for?

Characteristics 

No blemishes

MDF has a relatively hard, flat, smooth surface. It is more uniform that natural woods as it has no knots, rings or other blemishes. However, it is generally not as strong as plywood, tending to sag more easily under weight.

Guard against splitting

Like natural wood, it may split when screws are driven in without pilot holes, but it’s an excellent material for cutting and shaping by hand or machine.

Smooth-shank nails and fine-pitch screws don’t hold well in MDF and screw retention in the edge of the material is poor – MDF tends to split most often when drilling and screwing in its edge, especially when using a tapered wood screw, which acts like a wedge to drive the fibres of the MDF apart. 

Dedicated screws

Special screws, with a coarse thread, are available for use with MDF.

Weight

MDF is heavier than its chief rivals, plywood and chipboard.

Sometimes irritating

Most MDF contains a substance called urea formaldehyde, which may be released from the material through cutting and sanding. Urea formaldehyde can cause irritation to the eyes and lungs. 

Keep out of water

Unsealed MDF is easily damaged by water, which can cause it to expand quite quickly.

How dense is it?

MDF has a typical density of 600-800 kg per cubic metre, in contrast to particle board (160-450 kg per cubic metre) and high density fibreboard (600-1450 kg per cubic metre). For applications where weight is a prime consideration, lower-density board is used – which usually means particle board, also known as chipboard, or plywood.

How is MDF made?

Chipping

Softwood logs that have been stripped of their bark are passed through a chipper machine that chops the wood into small pieces. 

Other materials

Sawdust and recycled chips may also be added. Some manufacturers add other materials, including expired telephone directories, old newspapers and recycled cardboard cups.

Pulping

The material is then fed into a defribrating machine, which breaks down the wood into its most basic and smallest parts, known as pulp. The pulp is passed to a conveyor belt and sprayed with wax and resin glue. The wax makes the material more water-resistant and the resin binds it together.

Mat

The pulp is formed into a thick mat in a machine called a pendistor, exiting at a consistent thickness onto another conveyor.

Compression

After being rough-cut, the panels are fed into a press where a high temperature and extreme pressure compress the panels to the final desired thickness.

Finishing

After cooling, the MDF panels are cut to final finish sizes and both faces are passed through a large sanding machine to complete the process.

Binder

The most common binder for boards intended for dry environments is urea-formaldehyde. Other binders may be used depending on the grade of board and its intended end-use.  .

For example, melamine urea-formaldehyde, phenolic resins and polymeric diphenylmethane diisocyanate (PMDI) are generally used in boards that require an improved moisture resistance.

What are the different types of MDF?

Standard MDF

The most common, and cheapest, is standard interior grade material, suitable for most internal applications where moisture is not a consideration.

Moisture and fire resistant

Other types of MDF include moisture-resistant and fire-retardant grades. 

Exterior MDF

Exterior grade MDF can be used externally for cladding or signage work.

Pre-finished

There’s also melamine- and acrylic-faced MDF – pre-finished board available in plain colours, woodgrains, stone and metal effects for use in kitchens, bathrooms, furniture and shop-fitting.

What sizes are available?

MDF comes in large sheets, typically 4ft X 8ft (1220mm X 2440mm), although some can be as long as 10ft (3050mm).

It’s available in a range of thicknesses, from ⅛ inch (3mm) through to 1¼ inches (about 30mm). MDF at any thickness is easy to machine and provides an ideal painting surface.

What standards are there for MDF?

British and European standards

The current British Standard for MDF manufacture is BS EN 622-5:2009, titled “Fibreboards – Specifications – Requirements for dry process boards (MDF)”.

There are also European standards for MDF and the adhesives used to make them – manufacturers who prove that they comply with these standards can use the CE mark on their products.

Sustainability

You might also want to check that the wood content of any MDF you buy comes from sustainable sources.

What alternatives are there to MDF?

High density fibreboard (HDF), particle board and plywood are the main alternatives to MDF.

HDF

HDF contains more wood fibre per cubic metre than MDF, making it denser, and so heavier. It is used where extra hardness is needed, for instance as the core material for laminate flooring.

Particle board

Particle board, also known as chipboard, is made in a similar way to MDF but the wood component is in the form of small particles rather than fibres. At similar thicknesses, particle board is not nearly as strong as MDF, although it serves well for the construction of kitchen carcases and worktops when covered with moisture-proof vinyl. 

Standard MDF and particle board are prone to swelling across their thickness when they get wet, so should not be used in applications where there is a risk of water contact unless they are melamine or vinyl coated, or the MDF is the moisture-resistant type.

Even then, edges need to be perfectly sealed.

Plywood

Plywood is the strongest of the four types of board, due its construction – it is made up of several layers or “plies” of real wood glued together, with the grain of each ply at an angle, usually 90 degrees, to adjacent plies, giving it stregnth in all directions. It is better for construction work where strength is needed, but is more expensive than the other boards.

Of course, real wood is another alternative, but is considerably more expensive than manufactured boards and usually doesn’t come in handy sheets – lengths of real wood have to be joined together edge to edge to make a panel.

What type of manufactured board is most in demand?

Figures from the UK’s Forestry Stewardship Council (FSC) show that MDF is the most demanded fibreboard at 29%, with chipboard (particle board) a close second (26%), followed by plywood (20%) and high-density fibreboard (HDF) at 17%.

Advantages and disadvantages of MDF

• Generally cheaper than plywood

• The surface of MDF is very smooth and there are no knots on the surface

• Because it’s so smooth, it’s an excellent surface for painting – but be sure to use primer first

• MDF is consistent throughout, so cut edges look smooth

• It’s easy to cut into complex shapes using a scroll saw, band saw or jigsaw, and it can be routed 

• Versatile – useful in construction, interior design and craft work, and excellent for veneering to make furniture

• Just like particle board, MDF will soak up water and other liquids and swell unless it’s very well sealed on all sides

• Because it consists of such fine particles, it doesn’t hold screws very well

• MDF is very heavy – it’s difficult to lift large sheets without help

• It can’t be stained – it soaks up stain like a sponge and there’s no wood grain in MDF

• MDF contains urea-formaldehyde which can cause irritation to eyes and lungs – care needs to be taken when cutting and sanding