Microstructured Reflective\nCoatings on Commodity Textiles\nfor Passive Personal Cooling

As the effects of climate change become more severe and\nwidespread,\nmaintaining personal thermal homeostasis becomes necessary for survival.\nIn principle, advanced textiles and garments have the ability to leverage\nlight absorption, transmission and/or reflection, in addition to straightforward\nconvection, to heat or cool bodies in extreme temperature conditions.\nFor cooling, in particular, surfaces adept at selectively reflecting\nor refracting high-energy incident light (200 nm–2.5 mm) from\nthe sun while transmitting or emitting infrared light (8–13\nmm) from radiant body heat boast the ability to maintain cooler body\ntemperatures, even when exposed to direct sunlight and the open sky.\nHere, we present a strategy to transform common clothing into implements\nfor passive personal cooling. As confirmed by Mie scattering calculations,\ncheap and biocompatible calcium carbonate and barium sulfate micro/nanoparticles\nare found to serve as suitable reflectors for radiative cooling. Finite-difference\ntime domain simulations reveal, surprisingly, that higher reflectance\nis achieved with surface coatings containing these materials, as compared\nto extruded metamaterial fibers containing CaCO<sub>3</sub> and BaSO<sub>4</sub> particles embedded within a polymer matrix. A stepwise process\ninvolving photoinitiated chemical vapor deposition and ion-exchange\ndriven crystal growth is used to create a lamellar composite coating\ncomprised of alternating CaCO<sub>3</sub> and BaSO<sub>4</sub> nano/microparticle\nlayers directly on the surface of common fabrics. A polyester poplin\nfabric coated in this manner shows a cooling ability of up to 8 °C\ncompared to an uncoated sample, achieving a maximum cooling of 6 °C\nbelow ambient temperature. Wash and durability testing of the lamellar\ncoating reveal no mechanical degradation and no evident attenuation\nin the material’s performance, affirming its resilience and\nlong-term effectiveness as a functional textile coating for personal\ncooling. We also assess the performance of our coated fabrics in multiple\noutdoor environments to conclude that we can achieve up to 3.4 °C\nof sub-ambient cooling in optically complex built environments.