Polyester films which comprise not only thermoplastic polyester, e.g. polyethylene terephthalate, but also from 5 to 45% by weight of poly(m-xyleneadipamide) and optionally from 0.02 to 1% by weight of fillers, and which have, on at least one surface, an adhesion-promoting layer comprised of a hydrolyzed amino-functional silane. The films of the invention are produced by a sequential stretching process, and feature improved mechanical properties, such as a modulus of elasticity greater than 3500 N/mm.sup.2 in both orientation directions, high gloss, low haze, and very good barrier properties with respect to oxygen transmission. Films of the invention are therefore a suitable packaging material for foods and other consumable items, and as starting material for production of laminates via extrusion coating.