Many wearable devices fail due to suboptimal attachment interface design, leading to a lack of safety and ergonomics during physical human-robot interaction (pHRI). A better human-centered approach for attachment interfaces must include human properties in the design process. In this project, I propose to use soft tissue stiffness to design a variable stiffness forearm attachment interface. Discrete foam padding on the forearm cuff will be matched to the soft tissue stiffness at the corresponding location. This design approach will be evaluated using pHRI performance metrics such as kinematic misalignment, distributed interface loads, and interface energy loss.