The vapour diffusion barrier films offered specifically for the building industry are aluminium foils laminated with PET and/or PE films. These composite films have a WDD value of < 0.05 g / (m2d) and an Sd value of > 1500 m and are therefore classified as water vapour impermeable in accordance with DIN EN ISO 12572. Special composites comply with building material class B2 according to DIN 4102-1.