Enhanced radiative cooling paint with broken glass bubbles

In this warming world, radiative cooling is believed to be one of the most promising techniques for keeping cool without increasing greenhouse gas emissions. Glass bubbles have been proposed as a component of high-performance radiative cooling paints because of the bubbles' controllable size and their enhancement of light scattering. However, the current radiative cooling paints with glass bubbles suffer from low solar reflectivity because of their large particle size. In this study, we propose the idea of breaking the glass bubbles by means of ball milling to enhance the cooling performance of radiative cooling paints. The ball-milling process increases the solar reflectivity from 93.3% to 97.3% with the thermal emissivity of ∼93.4%, while the temperature difference with the ambient air is increased from 1.8 °C to 3.5 °C at noon. When the paint is covered with nanoporous polyethylene film, the temperature is 8.5 °C below the ambient air temperature at noon and 14.1 °C at night. The superior radiative cooling capability of the paint and the record-setting temperature difference achieved in Hong Kong demonstrate its excellent cooling performance, while the simple preparation method and ease of application make this paint promising for commercialization and large-scale production.