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 employs only comfortable and durable fiber materials. By designing a hierarchical nanofiber sheath around 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 increase in cooling power by 226 W/m² and a reduction in skin temperature by 7.0 °C compared to commercial fabrics under intense solar exposure. Moreover, the metayarn fabric exhibits exceptional 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 cooling textiles.