This paper presents a large-scale empirical study of OpenIDEO, an online collaborative design community. Using network analysis techniques, we describe the properties of this collaborative design network and discuss how it differs from common models of network formation seen in other social or technological networks. One major finding is that in OpenIDEO's social network the highly connected members talk more to less connected members than each other—a behavior not commonly found in other social and collaborative networks. We discuss how some of the interventions and incentives inherent in OpenIDEO's platform might cause this unique structure, and what advantages and disadvantages this structure has for coordinating distributed design teams. Specifically, its core-periphery structure is robust to network changes, but is at risk of decreasing design exploration ability if the core becomes too heavily clustered or loses efficiency. We discuss possible interventions that can prevent this outcome: encouraging core members to collaborate with periphery nodes, and increasing the diversity of the user population.