The pressure wave propagation method is applied here to the study of charging and discharging processes of polymer films of spatial interest. The irradiation of the materials is performed by a monoenergetic electron beam in the range 5–50 keV. Since the irradiated surface of the sample is free, we extended the model of the induced signals, previously developed, to take into account the total reflection of the pressure at the polymer‐vacuum interface. All the experiments, irradiations and measurements, are operated in a vacuum environment. After the description of the experimental setup, typical signals showing the interfacial effects are discussed. They concern the behavior of the sample‐vacuum interface and charge injection at the target‐sample interface. These experiments, which were carried out both on metallized and nonmetallized samples bonded to the target electrode, allow a direct observation of charge injection at interfaces.