Eco-oriented makers and grassroots subcultures experimenting with new technologies and ways to design sustainable futures are increasingly the subject of research. As activists address problems of environmental sustainability beyond institutional contexts, their work may appear vague, even confused, yet their activities are underpinned by intense and principled commitment. Working through their confusion, many DIY maker communities build new understandings about what ‘sustainability’ could mean. We argue that herein lie important resources for new knowledge and, further, that ethnography is the ideal way to track these processes of learning and knowledge production. The ethnographer participates in local confusion over values and the definitions of sustainability, but also about what constitutes useful knowledge. Supported by STS (and other) literature on environmental expertise, we argue that maker communities’ own acknowledgement of this vagueness actually makes possible a position from which epistemological authority can be reasserted.