Current approaches to personal medical product design address complex governance, technical and functional issues. However, little attention has been given to broader perceptions of the social and interpersonal issues related to medical products despite community attitudes playing an important role in supporting or inhibiting treatment uptake. Rethinking personal medical product design in light of the complex social contexts that they inhabit is needed to improve their desirability and subsequent uptake. Using the Continuous Positive Airway Pressure (CPAP) therapy mask when used to treat Obstructive Sleep Apnoea (OSA) as one example of a personal medical product, this study explored the social construction of breathing interfaces, by taking a critical approach to the design process. The purpose was to investigate how identification of the social and, relational understandings that are integrated into the design process and the product itself could be used as a tool to rethink and develop new possibilities for breathing interfaces and people with OSA. This study explores the application of a post-structural philosophical approach to a live design project based on the work of the French philosopher Michel Foucault. Data is in the form of discursive texts. These texts are analysed using adapted Foucauldian discourse tools in combination with design tools and approaches. Texts for analysis include: 1) Existing literature on OSA, breathing masks (including the CPAP therapy mask) and patient experiences of them; 2) a CPAP therapy mask and packaging; 3) a total of 11 semi-structured interviews with clinicians and community advisors; 4) community market-based exhibitions of critical probes, involving culturally probing interactions with 50 passers-by; and 5) notes and reflections from design explorations, scoping conversations and clinic visits. Findings show that the design of the mask is constrained by discourses associated with Western situated cultural aesthetics, masculine occupations and scientific legitimacy. While ‘successful’ users are almost evangelical about the CPAP therapy mask for treatment of OSA, the analysis shows how the subject position of the ‘successful’ user is shaped by the CPAP therapy mask design, and that there are multiple tensions for those who do not achieve this subject position. Indeed, data from the community markets reveals the diversity of subject positions that exist in relation to the mask and who participate in its social construction. The market-based interactions highlight subject positions that have been previously overlooked in human-centred design and the discursive tensions that affect device perceptions and potential uptake. The findings of this study have highlighted design factors and effects (relating to uptake of a product) that have not been considered previously, and would not be accessible using current human-centred design approaches. The findings have highlighted important considerations specific to the CPAP therapy mask design, and the approach itself offers valuable material for the study of medical devices more generally. Indeed this may have even broader applicability in product design by presenting a method of appealing to a range of actual and potential future users, whose needs remain currently unmet.