A process of forming a fine stabilized transverse pleating or waving in a film or film assembly in a nip between two circularly or helically mutually intermeshing grooved roller (101) and (102), or such grooved rollers which are modified by indentations on the crests, in which the film or the assembly is stuffed into the nip by being supplied with a fine traverse pleating or waving either prior to or while entering the nip, such that the forces exerted by the intermeshing grooved rollers is adapted to produce the desired stabilization, whereas the stuffing of the film or film assembly is produced or assisted by an airjet through the nip acting essentially on the full width of the film as an airknife or as an array of closely spaced air filaments.
