Thermoelectric modules can be used for thermal energy harvesting. Common rigid thermoelectric stacks usually contain heavy metal alloys such as Bi2Te3. In order to substitute conventional materials and to reduce manufacturing costs, nontoxic, inexpensive and abundant materials using low-cost processes are first choice. This study deals with polymer composites consisting of a polysiloxane matrix filled with thermoelectric Sn0.85Sb0.15O2 particles in micrometer scale. Thin composite sheets have been prepared by doctor blade technique and the Seebeck coefficient, the electrical and thermal conductivity, and the porosity were measured. Platelet-type particles, consisting of Sn0.85Sb0.15O2-coated insulating mica substrate and globular Sn0.85Sb0.15O2 particles have been varied in size, coating thickness and were mixed with each other in different ratios. The filler content was varied in order to maximize the figure of merit, ZT, to 1.9 × 10−5 ± 4 × 10−6. Owing to their low raw material costs and the high degree of design freedom of polymer composites, one may use these materials in thermoelectric generators for remote low-power demanding applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 40038.