Vapor barrier film having increased elongation at break in the longitudinal and transverse direction and variable water vapor permeability

The use of a copolyamide as a vapor barrier in insulation systems of buildings (vapor barrier) that increased elongation at break in the longitudinal and transverse direction, and a value dependent on the ambient humidity water vapor diffusion resistance which made of a material on copolyamide, wherein the material is a a blend of one or more crosslinking agents and / or one or more polyolefin homopolymers and / or one or more polyolefin is modified copolyamide and at a relative humidity surrounding the vapor barrier foil atmosphere of 100% and an ambient temperature of 0 ° C a water vapor diffusion resistance in the range of 4.5 to 8 g / (m