Apparatus for producing plastic film, of the type in which molten plastic is extruded through an annular die to form a tubular bubble which is expanded by air blown into the bubble, and a collapsing frame for forming the bubble into a flat tube prior to passing the tube through a nip formed between rollers, in which opposed, converging reaches of endless belts are used for the collapsing. The belts have their upstream ends held by a pair of first rollers spaced apart on opposite sides of the bubble, and have their downstream ends held by a pair of nip rollers which hold the belts together to form a nip for the collapsed tube. Pulleys and a belt, or gears, are provided which rotatably interconnect the pinch rollers and ensure that the belts entering the nip travel at the same surface speed.