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This paper discusses a methodology to select materials which deliver the best performance for thermally actuated pneumatic and phase change microactuators. The material selection is based on performance metrics estimated using simple closed form solutions for classical linear elastic theory for axisymmetric plates/membranes and lumped heat capacity thermal models. Although the elastic moduli of the diaphragm materials dictate the volume expansion for a given temperature rise, their influence on the achievable pressure difference is much less. It is found that engineering polymers are most suitable for thermopneumatically actuated diaphragms for delivering large displacements and work for the achievable pressures at frequencies of a few hundreds of Hertz. The membrane stresses due to in-plane pre-tension are found to have an adverse effect on the actuator performance. The material issues which constrain the performance limits of phase change actuators are also assessed, and the promising characteristics of paraffin waxes for microsystem applications are discussed.