Contemporary sustainability issues require the integration of diverse knowledge to study and address them holistically. How interdisciplinary knowledge integration arises in teamwork is, however, poorly understood. For instance, studies often focus on either individual or team processes, rather than studying their interplay and thereby contributing to understanding knowledge integration in an integral manner. Therefore, in this study we aimed to understand how knowledge integration processes are shaped by interactions in interdisciplinary teamwork. We present insights from an ethnographic case study of interdisciplinary teamwork among eight master’s students. In this student team, we observed two dynamics that impeded knowledge integration: (1) conformative dynamic manifested as avoiding and ignoring differences, and (2) performative dynamic as avoiding and ignoring not-knowing. Based on earlier work, we expected that contributing one’s own and engaging with each other’s knowledge would ensure knowledge integration. However, the dynamics exposed that it did not only depend on whether knowledge was contributed and engaged with, but also which knowledge was exchanged and manipulated in the teamwork. We coin the concept ‘relative expertise’, which emphasizes that interdisciplinary teamwork requires that collaborators act simultaneously as expert—in relation to their own contributory expertise—and non-expert—in relation to others’ contributory expertise. The dynamics hampered acting as a relative expert, and we saw that this was shaped by an interplay of students’ individual epistemic competencies, shared assumptions about teamwork, and social context. The insights may help recognize dynamics and underlying factors that impair knowledge integration, and thereby inform targeted interventions to facilitate knowledge integration.