Purpose-Through the lens of the open innovation model and knowledge-based view (KBV), the present research seeks to investigate three key factors (i.e. cognitive dimensions, the knowledgedriven approach and absorptive capacity) that are likely to determine the preference for informal inbound OI modes. The innovation literature has differentiated these collaborations into informal inbound open innovation (OI) entry modes and formal inbound OI modes, offering an advocative and conceptual view. However, empirical studies on these collaborations are still limited. Design/methodology/approach-Building on the above theoretical framework, the empirical research was performed in two stages. First, data were collected via a closed-ended questionnaire distributed to all the participants from the sample by e-mail. Secondly, to assess the hypotheses structural equation modelling (SEM) via IBM® SPSS® Amos 20 was applied. Findings-The empirical research was conducted on 175 small to medium enterprises in the United Kingdom, suggesting that the knowledge-driven approach is the strongest determinant leading to a preference for informal inbound OI modes. The findings were obtained using structural equation modelling (SEM) and are discussed in line with the theoretical framework. Research limitations/implications-Due to the chosen context and sector of the empirical analysis, the research results may lack generalisability. Hence, new studies are proposed. Practical implications-The paper includes implications for the development of informal inbound open innovation led by knowledge-driven approach. Originality/value-This paper offers an empirical research to investigate knowledge-driven preferences in informal inbound open innovation modes.