Although informal knowledge networks have often been regarded as a key ingredient behind the success of industrial clusters, the forces that shape their structure and dynamics remain largely unknown. Drawing on recent network dynamic models, we analyze the evolution of business and technical informal networks within a toy cluster in Spain. Empirical results suggest that the dynamics of the two networks differ to a large extent. We find that status drives the formation of business networks, proximity is more crucial for technical networks, while embeddedness plays an equally important role in the dynamics of business and technical networks.