In the present work we investigate the processes of charge transport and storage in polypropylene films under isothermal conditions. The samples were manufactured either as solid films via heat-pressing, or as 3D-printed films in FDM filament printer. Isothermal surface-potential-decay measurements reveal much higher charge stability in 3D-printed samples. We attribute this to the increased number of interfaces, large surface area and, probably, surface modification via increased oxidation of said interfaces during printing.