Exploring the advancement of soft and variable impedance actuators (VIAs), the research focuses on their potential for enhancing safety and adaptability in physical human-robot interactions (pHRI). Despite the promising attributes of these technologies, their adoption in portable applications is still emerging. Addressing the challenges hindering the widespread implementation of soft actuators and VIAs, a multidisciplinary approach is employed, spanning materials science, chemistry, thermodynamics, and more. Novel compliant actuators utilizing phase-change materials and flexible thermoelectric devices are introduced, offering improved safety, adaptability, and efficiency. Thermo-active phase change soft actuators, integrating Peltier junctions, achieve precise thermal control and reversible actuation, overcoming traditional Joule heating limitations for more efficient and controlled thermal responses. The research also delves into thermal variable impedance actuators, using viscoelastic polymers like polycaprolactone (PCL) for variable stiffness and damping. This innovation enables rapid adaptation to changing load conditions, enhancing the dynamic performance of VIAs. Key contributions encompass the design of an agonist-antagonist system using thermo-active phase change materials, applications in soft robotic devices such as grippers and locomotion mechanisms, and the implementation of bidirectional heating elements within these actuators. The work also outlines the challenges encountered, such as gravity's influence on actuation and the frequency-dependent properties of PCL, setting the stage for future research directions to advance the field of soft robotics. Through these contributions, the research demonstrates practical applications of soft and variable impedance actuators in pHRI, paving the way for future innovations in soft robotics.