This article presents an analytical model allowing the determination of the, d33, piezoelectric coefficient in cellular polymer films. The cellular film is identified to an equivalent effective layered structure made of alternating gas and solid layers that are electrically charged at their interfaces. The model expresses the d33 piezoelectric coefficient as a function of porosity, film thickness, free-stress surface charge density, and the film modulus, which depends on frequency. The temperature is indirectly taken into account as it is involved in the parameters appearing in the final equation of the model. The obtained results showed that the piezoelectric activity of charged cellular polymer films decreases with the film thickness and increases with the film expansion and the surface charge density. The variation with the percentage of porosity shows a nonlinear trend, with an increase in the d33 piezoelectric coefficient with the void fraction, and then a decrease when such a percentage exceeds a thickness-dependent critical value. Such quantitative description of the piezoelectric activity can help the design of cellular films with enhanced piezoelectric performances. The model predictions were also compared with some experimental results obtained on cellular piezoelectric films made of polypropylene filled with 10% of calcium carbonate microparticles. POLYM. ENG. SCI., 2013. (c) 2012 Society of Plastics Engineers