In this paper, we discuss the requirements and critical challenges for creating and staging interactive costumes in the theatre. Different to other types of performance, theatre costumes are secondary to acting. Our investigations are based on two practice-based case studies: a self-directed design research within a student project, and a collaboration with a local theatre house, where interactive costume elements were developed in a real-life setting. These reveal requirements and challenges for the design process as well as the effective staging of interactive costumes, the biggest challenge being how to integrate these into existing structures of traditional theatre houses, and requirements for the costumes themselves. Because interactive costumes integrate technological features and traditional analogue crafts, they require interdisciplinary collaboration and transcend established boundaries between departments in theatre houses, challenging established work processes and structures.