Regulatory intermediaries—organizations that operate between regulators (public and private) and target groups—perform a range of important functions. While most previous research has focused on intermediaries that have been delegated official authority, in this paper we focus on unofficial and informal intermediary functions aiming to advance the governance of per- and polyfluoroalkyl substances (PFAS) chemicals. Chemical pollution is a growing environmental and health concern, leading to both public and private regulatory initiatives. By studying a particular segment—paperboard food packaging in Sweden—the study generates insights into critical functions performed by unofficial intermediaries (Svenskt Vatten and ChemSec) in this regulatory regime, which extend and expand regulatory reach in various ways. The study also shows the importance of different types of intermediaries that interact in dynamic ways, and the role of material artifacts in processes of intermediation. These unofficial functions are arguably important for the functioning of complex, hybrid forms of governance, but they also prompt critical questions about the effectiveness, legitimacy, and role of intermediaries in generating needed transformative change.