Dielectric elastomers have been widely investigated for muscle-like soft actuators and capacitive sensors. Mechanical properties play a central role in the performances of the active material. Most elastomers have specific moduli pre-determined by the polymers' molecular structures, which are not suitable for applications in changing working conditions as natural muscles are capable of. Here new dielectric elastomers are described exhibiting variable moduli controlled via thermal treatment. The elastomers contain furan-maleimide Diels-Alder adduct moieties to administer the crosslinking densities of the elastomeric networks via reversible Diels-Alder/retro-Diels-Alder cycloaddition reaction, resulting in changes in the elastomers' moduli. One of the synthesized elastomers has moduli that can be controlled between 0.17 and 0.52 MPa incrementally and reversibly. Capacitive strain sensors based on this elastomer can be operated in both rigid and soft modes to achieve variable sensing response up to 30% linear strain. Actuators were fabricated and operated in both high strain mode (35% actuation area strain at 65 MV m(-1)) and high force output mode (0.55 MPa at 104 MV m(-1)). The elastomers can exhibit a range of stress-strain outputs in similar fashion as muscle.