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 two sets of pleating rollers comprising intermeshing grooves or discs for pleating the material . the downstream rollers comprise a mini - roller defined by the following measures a ) the pitch of the corrugations , measured from middle of tip to middle of each neighbouring tip is 20 mm or less ; b ) the perimeter from middle of a tip to the middle of each neighbouring tip measured along the corrugated roller surface , divided by the said pitch is in the range between 1 . 10 and 1 . 80 ; and c ) the diameter of the mini - roller , measured at the tips of the corrugations , is at the highest 4 times the said pitch . preferably a pair of mini - roller sets is arranged on opposing sides of the film in reciprocating mounts enabling alternate entwining of the film around one then the other mini - roller . the method allows achievement of high tensile strength , yield point , resistance to tear propagation and puncture resistance , especially for polyethylene and polypropylene films .