Passive Radiative Cooling Designed Hexagonal Boron Nitride/Silk Fibroin‐Based Patch for Personal Thermal Regulation

ABSTRACT Natural silk textiles with passive radiative cooling properties show promising potentials for energy‐efficient personal thermal regulation. Herein, the thermal regulation patches (SF@Gly‐BN) based on silk fibroin (SF), glycerin (Gly), and boron nitride nanoflakes (BNFs) are fabricated. The incorporation of BNFs enhances the solar reflectance from ~0.3 to ~0.7 in the high solar spectrum region while maintaining a high infrared emissivity of ~0.85 in the mid‐infrared region for SF@Gly‐BN patches. The enhancement of these optical properties endows the SF@Gly‐BN patches with excellent passive radiative cooling performance. Indoor tests show a ~14.7°C sub‐ambient temperature drop for the SF@Gly‐BN patch with 20 wt% BNFs, whereas the outdoor testing exhibits an average sub‐ambient temperature drop of ~14°C on the clear days with the average solar irradiance of 1050 W m −2 . Moreover, the SF@Gly‐BN patch shows great potentials for personal thermal regulation which can reduce skin temperatures by ~6.5°C and ~3.0°C respectively in outdoor and indoor conditions. This research offers an approach to developing efficient, eco‐friendly, and biocompatible wearable thermal management products.