A Hierarchical Nanofiber-Sheath Engineered Daytime Radiative Cooling Metayarn

Incorporating radiative cooling photonic structures into textiles offers an eco-friendly and effective solution to mitigate the growing impact of global climate change on human comfort and health. Traditional fabric materials, however, typically feature fiber diameters in the tens of microns range, which are not matched to the wavelength of sunlight. This mismatch impedes efficient photon interaction necessary for daytime radiative cooling. Herein, we report a cooling metayarn that solely employs comfortable and durable fiber materials. By designing a hierarchical nanofiber sheath on a natural fiber yarn core, we endow traditional yarns with photonic interactivity. This yarn is compatible with existing textile manufacturing systems. The resulting fabric demonstrates high infrared emissivity (95%) in the atmospheric window and high reflectivity (94%) in the solar spectrum. This leads to an extraordinary cooling power increase of 226 W/m2 and a skin temperature reduction of 7.0 °C compared to commercial fabric under intense solar exposure. Moreover, the metayarn fabric exhibits exceptional comprehensive wearability, including flexible color designability, excellent photonic structure stability, and satisfactory comfort. This method of enhancing conventional textile yarns with a nanofiber photonic sheath structure opens new avenues for the development of sustainable smart textiles and advanced radiative cooling applications.