Cellular polymer foams with significant piezoelectric activity were prepared from fluorinated ethylene-propylene (FEP) copolymers. The required void structure is obtained by saturation of FEP films with supercritical carbon dioxide and a subsequent heat treatment for controlled inflation. After bipolar electric charging of the voids and evaporation of electrodes, the FEP films show piezoelectric d33 coefficients up to 50 pC/N. The present physical foaming process generates cellular fluoropolymer piezoelectret films with usually only one single void across the film thickness.