This thesis describes a study into Electromechanical Film (EMFi) of polypropylene (PP). The reported results were obtained from an extensive investigation which included the characterisation of the polypropylene itself, its cellular structure as well as the mechanical, electrical and piezoelectric properties of the material. In particular, the study investigated the dependence of these properties on temperature. Based on cross-section SEM micrographs, the cellular structure was characterized in terms of the associated magnitudes such as anisotropy ratios (R12 = 1.69, R13 = 7.96 and R23=4. 71) and cell wall thickness. Thermo-mechanical analysis (TMA) revealed t hickness-mode Young's modulus, Y3, ranging from ~ 0 to ~ 50 KPa which is unusually low for close-cell foams suggesting that a significant leaka.ge of gas out of the foam occurs when the foam is compressed. TMA also revealed the low thermo-mechanical stability of the material whose cellular structure starts to collapse at ~ 60°C. Charge stability was a lso investigated using the Thermo stimulated current (TSC) technique. The TSC curves showed the depolarisation of the material starting at 60°C and the inital rise method yielded an activation energy of~ 2 eV suggesting that the depolarisation arises from the charge detrapping. The piezoelectric nature of the foam was investigated in terms of the piezoelectric d3J coefficients and resonator parameters such as electromechanical coupling factors, acoustic absorptions and sound velocities, obtained by fitting t he measured values of the complex capacitance to the theoretically predicted expression close to the piezoelectric resonances. Especial emphasis was placed on the thermal instability of the piezoelectric property. The Young's moduli, Yi, ½ and Y3 for the foam, extracted from the resonator parameters were observed to reversibly decrease with increasing temperature because of softening of the polymer. It was a lso observed that the values of the moduli measured after annealing increased irreversibly for anneal temperatures above 60°C suggesting the collapse of the cellular structure. Based on the obtained results, we propose that the thermal instability of the foam relies on both the depolarisation of the material by charge detrapping and the thermal instability of t he cellular structure which leads to a collapse of t he voids.