Cross-linked polypropylene (XPP) foams are modified by a hot-stretching process and charged to be piezoelectric. The results show that a piezoelectric d 33 -coefficient of 308pC/N is obtained for sample with an elongation ratio of 200%. The dynamic d 33 value is smaller than the quasi-static value, which is probably due to the rise of Young’s modulus with increasing frequency. All the samples show pressure-independent d 33 in the range up to 30 kPa. Improved d 33 was obtained in the sample rough surface exposed to the corona during charging. Compared to linear PP, the stretched XPP shows pressure independence of d 33 in larger range.