Social network theory has produced conflicting results regarding the link between different social network structures-bridging versus bonding-and idea generation. To address this conundrum, we conduct a naturally occurring quasi-experiment of 126 open and 108 closed groups within an Enterprise Social Media (ESM) system of a multinational enterprise. Our findings show that idea generation occurs when the type of social network structure-bridging or bonding-is matched to a group's openness or closedness, respectively. We further show that the reverse is counterproductive: when closed groups display bridging ties and open groups display bonding ties, idea generation is significantly undermined. Theoretically, these findings clarify the conditions and mechanisms by which both bridging and bonding can result in idea generation and provide a deeper understanding of the use of ESM for idea generation. Practically, our findings provide valuable and actionable insights regarding the use of ESM for idea generation in groups.