Medium density fibreboard (MDF) is made by heating wood under pressure until the fibres and natural glues that bond them together soften.

Then the fibres are rubbed apart, combined with glues and additives, and pressed into sheets.

The process is similar to particleboard manufacture, except that particleboard is really a 'low' density fibreboard and is made from wood chips rather than fibres.

MDF as an underlay product

The typical sheet size for MDF underlay is 1220 x 915 mm (4 ft x 3 ft), with a thickness of 5 mm. However, many other sizes and thicknesses are also available.

Although MDF is manufactured in both 'standard' and MR (moisture resistant) grades, it is still not recommended for floors in wet areas, or where wet processes are used to bed down the tiles.