MDF is manufactured in a "dry process" with a synthetic adhesive. Boards are categorised according to their density: High Density Fibreboard (HDF) with a density ≥ 800 kg/m³, light MDF (L-MDF) with a density ≤ 650 kg/m³ and ultra light MDF (UL-MDF) with a density ≤ 550 kg/m³. By changing the composition of the synthetic binder or by incorporation of other additives enhanced properties can be provided. Properties such as fire resistance, moisture resistance and resistance against biological attack can be altered. Vapour permeable fibreboards are a special product within the range of fibreboards. Moisture can easily pass through the permeable boards to the outside. Often tongue and grove profiles on two or four sides of the board, simplify installation of these panels in practice.