Disclosed is an improved process for extruding films of thermoplastic polyester film-forming materials. The process enables extrusion of films with reduced problems of neck-in, edge-weave and beading, by feeding a small amount of a polymer which is readily processable with the polyester into the extruder die in the area near the edges of the elongated die opening. The different polymers commingle at the edge portions and thereby provide a controllable edge. In the preferred embodiment, a small amount of a low-to-high density polyethylene is injected into the film-forming die near the edge portion of a stream of polyethylene terephthalate prior to extrusion. The resulting milky-appearing edges are preferably cut from the film, and the film is then adhered to a paperboard substrate.