Bridging Horizontal to Vertical Radiative Cooling.

Radiative cooling materials enable sub-ambient passive cooling but are typically limited to horizontal surfaces such as rooftops, restricting their use in dense urban environments where vertical facades dominate. Here, we develop a scalable BSDAR bridging system that enables existing radiative cooling materials to function effectively on vertical surfaces. The system redirects thermal radiation toward the sky while suppressing heat gain from surrounding buildings and the ground. On vertical windows coated with polydimethylsiloxane, daytime reductions of up to 4.1°C below ambient are reached with a wind shield and thermal insulation, while a window on a real building in an urban canyon, operating without either, remains 1.2°C-1.4°C below ambient. The BSDAR bridging system preserves daylight transmission, exterior visibility, and seasonal tunability. This approach extends radiative cooling from rooftops to glazed elements of vertical facades at all orientations, supporting more sustainable cooling strategies for urban buildings.