method and apparatus for longitudinal orientation of thermoplastic film material comprises a width - reduction zone upstream of the longitudinal stretching zone , through which the width of the film is gradually reduced so as to allow longitudinal stretching without necking . the width - reduction zone comprises at least one , preferably several , pairs of pleating rollers comprising intermeshing grooves or discs for pleating the material , the length of said width reduction zone preferably being less than 3 times the original width of the film . the width - reducing zone has upstream and downstream rollers or roller assemblies , with curved axes and optionally also conveyor belts for providing smooth width reduction . longitudinal stretching is preferably between at least two , and preferably more than two , pairs of stretching rollers which are relatively close together . the pleats may be provided in several stages with increasing pleats per stage , while guiding means preferably lay all the pleats to one side . the method allows achievement of high tensile strength , yield point , resistance to tear propagation and puncture resistance , especially for polyethylene and polypropylene films .