Medium Density Fibreboard . It is dense, flat, stiff, has no knots and is easily machined. Because it is made up of fine particles it does not have an easily recognisable surface grain. It can be painted to produce a smooth quality surface. Because it has no grain it can be cut, drilled, machined and filed without damaging the surface. Oil, water-based paints and varnishes may be used on MDF. veneers and laminates and digital vinyl prints may also be used to finish the surface. MDF is used predominantly for interior signs.