Dielectric elastomers (DEs) constitute a class of electroactive polymers that are becoming increasingly important as lightweight and mechanically robust replacements for conventional transducers and actuators. Because of their inherent cycling resilience, they also show tremendous promise as energy-harvesting media, as well as smart sensors and microfluidic devices. Recent studies have demonstrated that DEs composed of midblock-solvated triblock copolymers exhibit attractive electromechanical attributes such as giant electroactuation strains at relatively low electric fields at high conversion efficiency. Moreover, the properties of these readily processable systems are highly composition-tunable, thereby making them ideal candidates for a detailed study of the coupling between initial specimen thickness and mechanical prestrain, which is frequently used to reduce specimen thickness before actuation to lower the voltage required to achieve electroactuation. Conventional wisdom based on the notion of an ideal DE indicates that electroactuation should only depend on pre-actuation specimen thickness, but we report results that unequivocally indicate a more detailed material/process description is required. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1569-1582, 2011