My dissertation is an ethnographic case study of acts of making at SoDo Makerspace in Seattle. There is interest in making and materiality across rhetoric and writing studies, and this calls for a robust understanding of mattering—in both the material sense and the semiotic sense—in acts of making. We have a rich tradition of studying what matters in acts of making (in terms of language, culture, socio-economics, and access), and much of this work turns to reflection and mediation as frameworks for teaching and studying mattering. Many useful insights have emerged from these approaches, but there are limitations to these frameworks: both reflection and mediation tend treat the thing being reflected or mediated and the person and tools doing the reflecting and mediating as more-or-less separate, even pre-existing entities. I argue that this can cause us to miss an important part of what matters in acts of making, which is the marking of boundaries: how "writing" or "rhetoric" or "making" or "maker" comes to be marked as such in the act of making. Understanding mattering in this way, as boundary marking, can offer us a more complex understanding of acts of making. Studying mattering and making in this way presents a methodological challenge, and I turn to feminist and decolonial work to develop a genealogical approach to studying mattering, for studying the complexity and entanglement of what matters and what is excluded from mattering in acts of making. Over a series of genealogies, I trace mattering and making—of objects, rhetoric, knowledge, and makers—in the makerspace over the course of a year of fieldwork, and I offer implications for theorizing and teaching writing and rhetoric.