Colloidal Photonic Fibers for Reflectively Colorful Radiative Cooling Fabrics

Daytime radiative cooling has emerged as a promising passive strategy for sustainable thermal management, yet its widespread implementation remains hindered by the lack of colorful, transformable, and scalable material systems. Here, we present a new class of structurally colored radiative cooling fibers created by microfluidic extrusion of mid-infrared (mid-IR)-emissive colloidal structural fluids. These fluids consist of monodisperse silica (SiO₂) nanoparticles (NPs) suspended in an acrylate resin, which self-assemble into amorphous photonic glass during microfluidic shear flow and are subsequently solidified by in situ photocuring. The resulting fibers exhibit angle-independent and permanent structural coloration across the visible spectrum, which is tunable via NP size and interparticle spacing without the use of pigments or dyes while maintaining broadband mid-IR emissivity (>0.9) arising from SiO₂ phononic vibrations. When woven into fabrics, these photonic fibers combine high solar reflectance with strong mid-IR thermal emission, enabling effective reduction of solar heat gain and daytime cooling of a heated skin-mimicking substrate even under direct sunlight. Outdoor tests confirm that photonic glass textiles achieve a large temperature depression on simulated skin phantoms, consistent with their broad visible scattering and high mid-IR emissivity. This work introduces a scalable and esthetically versatile route toward colorful radiative-cooling textiles, bridging photonic design with practical energy-saving applications in outdoor and wearable systems.