The two-stage drawing of uniaxially oriented poly(ethylene terephthalate) (PET) films has been undertaken, together with the drawing of films at constant width, which are biaxially oriented, under equivalent conditions of temperature and strain rate. From measurements of the changes in refractive index, drawing stress and peak shrinkage stress, it is concluded that the behaviour can in all cases be described by the deformation of a molecular network, which is of a very similar nature not only for all these present measurements but also for previous studies of PET fibres and films.