Wearable robots enhance the ability of their wearers to physically interact with the world, and can benefit rehabilitation efficiency, assistive devices’ effectiveness, and ergonomic support of workers. Wearable robots’ ergonomics and safety can be promoted by using actuators made of soft materials, but soft actuators in the literature are unable to produce the high torques required for lower limb activities of daily living (ADLs), for example, extension of the knee for sit-to-stand. This paper presents and validates a method for realizing a soft high torque actuator, the pleated pneumatic interference actuator, for knee extension. It was shown to produce a torque of 150 Nm at 2 bar and an angle of 70°. Future work will see the development of a portable pressure source to inflate the wearable actuator.