Progress on Natural and Sustainable Materials for Daytime Radiative Cooling

Daytime radiative cooling has gained recent momentum in the field of sustainable cooling technology. Due to its passive nature, metamaterial development is a crucial requirement for further advancement in performance and application. Various structural materials have been developed to date; however, for simplicity and facile manufacturing, a polymer–particle structure is considered the most suitable metamaterial for radiative cooling. Other material structures are substrate dependent and are complex to produce. To increase sustainability, a polymer–particle structure with a natural polymer is becoming a rapidly growing field, which could be derived from natural resources like wood, pulp, and some natural fibers. Hence, in this paper, material structures and their outcomes are critically reviewed, and a special focus is made on natural and renewable materials. It is found that natural polymer-based materials have comparable thermal performance compared with commercial polymers. Apart from performance, sustainability aspects of various materials are elaborated in detail. Some transparent wood-based materials for building window applications are also included because of the recent need for energy-efficient buildings. The natural polymer-based radiative cooling coatings are environmentally friendly, processed from natural resources, and applied to renewable cooling technology, ther…