This study investigates whether a meeting environment’s visual openness influences team productivity and communication quality. We conducted a randomized controlled trial with participants assigned to discussions held in a transparent glass meeting room (treatment) or a fully curtained room (control). Team productivity was evaluated based on the quality of participants’ policy proposals. Communication quality was assessed using transcript-based indicators such as laugh frequency and topic diversity. We found that groups in visually open meeting rooms received significantly higher proposal ratings and exhibited greater emotional positivity and topic diversity, highlighting that within-session dynamics expose how environmental design affects group interaction.