This paper explores how design and commoning practices can contribute to sustaining open cultural commons and guarding against enclosure. Based on a long-term engagement with a cultural movement, the author examines how design activities can strengthen interaction and participation in commons-like frameworks, and describes commoning and instrastructuring practices that can support commons culture. By critically reflecting on the development of a local Finnish chapter of the OpenGLAM (Galleries, Libraries, Archives and Museums) movement, the paper contributes to the ongoing discussion of design as infrastructuring in complex and open-ended socio-technical settings.