Multi-layer polyolefin films for envelope windows, comprising at least three layers wherein the central layer comprises a propylene homopolymer; the layer of film on the outer part of the envelope, which forms the anti-reflective layer, is based on propylene copolymers in mixture with HDPE, HDPE being comprised between 40 and 50% by weight of the mixture; the inner layer in contact with the contents of the envelope is based on ethylene/propylene/butene copolymers, the film being isotropic in relation to shear strength.