In this article, the reversible and irreversible thermo-mechanical time-dependent deformation of oriented polyethylene terephthalate film is studied. A mean-field model is used to simulate these effects along with the long-term creep behaviour, taking into account the underlying material microstructure and differences in constitutive behaviour of the phases. The material is modelled as an aggregate of layered two-phase domains. Irreversible deformation, or partial shape recovery, results from the presence of an internal stress, which is characterised and incorporated into the constitutive behaviour of the non-crystalline phase. Using the micromechanical approach, the deformation mechanisms at the local scale are analysed.