Highly Efficient Polystyrene/Metal Oxide Fiber Composites for Passive Radiative Cooling

Passive radiative cooling has garnered significant attention in energy‐saving applications as it is an effective way to cool to temperatures below ambient without external energy input. Successful cooling performances can be achieved by carefully selecting metal oxides with narrow absorption bands that lie entirely within the atmospheric window of 8−13 μm, thereby allowing radiative transfer between terrestrial objects and outer space. Highly scalable, metal oxide‐doped fibers made from recyclable polystyrene herein are proposed and demonstrated. The material exhibits nearly 100% reflectivity in the visible and near‐infrared (IR) range, and under direct solar irradiation, the material can cool by up to 22.3 °C below the ambient temperature without energy input due to strong emissivity in the atmospheric window. This cooling persists despite nonideal atmospheric conditions and convective/conductive heat exchange. Microsized fiber‐based radiative cooling is reported for the first time. Unlike film‐based passive radiative cooling materials, fibers are relatively simple to manufacture, flexible, lightweight, and low in cost. Therefore, such a material may be suitable for large‐scale applications such as buildings to supplement air conditioning or as a wearable fabric to promote subambient cooling for the wearer.