Dielectric elastomer (DE) actuators exploit electrically induced deformations of insulating rubbery materials, as a means to transduce electrical energy into mechanical work. To enable large deformations, recent studies have demonstrated the advantage of either using elastomers that suppress pull-in electromechanical instability or driving the actuator at the verge of instability while still preventing it. Whenever these strategies are not applicable, softening the material remains the mechanical approach of choice to enable large deformations at relatively low electric fields. As the most common approach to lower the elastic modulus of an elastomer is the use of plasticizers, understanding their effects also on other properties of the elastomer is important, especially to actuator designers. Aimed at gaining insights in this respect, this paper presents an extensive chemical–physical, dielectric, mechanical and electromechanical characterization, for different amounts of a plasticizer, of one of the softest commercial silicones demonstrated for DE actuation (elastic modulus of the order of 100 kPa). The results showed the interplaying effects of a variable addition of the plasticizer, elucidating key features that could thus serve as a guide to the design of actuators for specific needs.