Innovation management research has recently pointed out that competitive advantage depends on the ability to connect knowledge at both intra- and inter-organisational levels through multiplex boundary work. Resource-based view (RBV) and knowledge-based view (KBV) can provide valuable and complementary insights to understand which individual-level determinants enable knowledge exchange through collaborative boundary work. Based on these arguments, we adopt a microfoundational approach to explore, through a multiple-embedded case study of seven small- and medium-size enterprises (SMEs), the individual characteristics that make organisational members able to connect across boundaries and perform effective multiplex boundary work for collaborative innovation. Our findings show the relevance of three sets of individual determinants (i.e., openness to others, assertiveness, and balancing skills). This study extends the RBV and the KBV by identifying the main individual determinants that represent an essential resource base for leveraging internal and external knowledge in SMEs' engaging in multiplex boundary work for collaborative innovation.