Diffusion-open sub-roof film made of 3-layer film composite with UV-resistant special membrane made of highly elastic TPU. As a sub-roof for ventilated pitched roofs with normal loads as well as with waterproof bonding for sub-roofs with increased loads according to SIA 232/1. For direct support on wooden formwork, soft fibre boards or thermal insulation for between- and above-rafter insulation systems as well as for use in canopy areas. Basis weight 205 g/m2.