Abstract: A transverse stretching device comprises two stretching wheels and endless bands arranged against them and revolving around band guide rolls so that a plastic film to be stretched is arranged at its both edges between a stretching wheel and a band. The stretching wheels and the bands are arranged in such a way that in the direction of travel of the plastic film they are further apart from each other at the end than in the beginning, whereby the transverse stretching device stretches the plastic film in the transverse direction. The stretching wheels are rims open in the center and the device includes heating means arranged through the rims at least at some angle between the stretching wheels.

Abstract: A film (5) is extruded from plastic material by means of an extruder. Material is mixed into the plastic (5a) of the plastic film (5) before the extrusion so that cavitation bubbles are formed in the material particles mixed into the plastic (5a) when the plastic film is stretched. The film (5) is orientated by stretching. After the extrusion the plastic film (5) is cooled slowly below the crystallization point of the plastic material before the orientation.