Most robots are unclothed. However, we believe that robot clothes present an underutilized opportunity for the field of designing interactive systems. Clothes can help robots become better robots––by helping them be useful in a new, wider array of contexts, or better adapt and function in the contexts they are already in. In this paper, we provide a foundation for a research area of robot clothing by speculating on its potential. We systematically present functional requirements of robot clothing, considerations, and parameters for robot clothing designers, as well as key reference cases of robots in clothes. We then discuss what robot clothes can do specifically for the field of designing interactive systems.