Low cost, large area, lightweight, stretchable piezoelectric films, based on space-charge electret with a foam structure (i.e., ferroelectrets or piezoelectrets), have been fabricated by using commercially available irradiation cross-linked poly(propylene) (IXPP) foam sheets. Piezoelectric d33 coefficients are as high as 100 pC · N−1. The piezoelectric performance in such IXPP films is well preserved for repeated strains of less than 10%. Piezoelectric d33 coefficients are frequency independent in the range from 2 to 100 Hz. Such new class materials may be applied in sensory skins, smart clothing, bio-inspired systems, microenergy harvesters, and so on.