Nowadays, thermoplastic polymers do not cease to attract the interest of the industrialists as steel / polymer composites for various applications in several domains, such as the automotive and the packaging. The ratio between their wide range of thermo-mechanical properties and their low weight density make these materials a real alternative for the current solutions for the lightening and the reinforcement of structural pieces. Likewise, their working facility is a major asset for performing parts of complex geometry. In this paper, we highlight the narrow relationship between the microstructure of a small impact isotactic polypropylene film, either filled or not by mineral particles (calcite), and its behaviour towards shrinkage which can occur during thermal treatments above its melting temperature. This phenomenon of shrinkage is characterized by dimensional instabilities which can in particular, affect the life cycle of the material. Indeed, they may induce the partial delamination of the steel sheet which is consequently exposed to various environmental aggressions. Corrosive behaviour can occur and cause early breakdown of the material. Influences of the extrusion and stamping processes on the microstructure and the shrinkage are presented. The macromolecular chains orientation of the crystalline phase, the volume damage and the heating parameters are studied, and show a real impact on the phenomenon magnitude. An experimental setup was developed at the laboratory to measure in real-time and with good precision, the displacements induced by shrinkage and the microstructural evolution of the polymer film during different thermal cycles. Finally, an empirical law allowing the shrinkage prediction is presented, taking into account the deformation value and the initial degree of chains orientation. These studies and their results have led to the determination of the optimal parameters settings for the different conformation processes with the aim of reducing the maximum of shrinkage.