The invention relates to a foil consisting of at least two layers and made of thermoplastic polyurethane with directional water vapour permeability. The water vapour permeability of each of said foils varies depending on which of the two outer layers of the foil faces the moisture source, when water vapour permeability as determined in accordance with DIN 53122, measured across the total density of the foil. The thermoplastic polyurethanes used for the foil are made of possibly hydrophilized rigid segments consisting of diisocyanates and low-molecular diols as chain extenders, and of soft segments consisting of bifunctional polyols, the latter being high molecular polyethers and/or polyesters.
