Despite considerable research interest in developing piezoelectric materials, little work has focused on the fundamental design of these materials from the ground up. Herein, we present a general, versatile method for producing tunable, flexible piezoelectric energy harvesters (PEHs) with excellent piezoelectric response. Using a poly(dimethylsiloxane) (PDMS) foam derived from a sugar template, we separate the electrical and mechanical properties of the PEH, thereby allowing us to optimize them separately. The electrical properties were tuned by varying the poling field, the polar dopant, and the dopant concentration. The mechanical properties were tuned by varying foam preparation and thus the compressive modulus. Through the careful tuning of these properties, we are able to achieve a maximum piezoelectric response of 153 pC/N—considerably higher than most other reported flexible PEHs. Combined with our previous work, we demonstrate that doping polymer foams with polar dopants is a highly general strategy and has the potential to lead to materials with considerably higher piezoelectric responses.