Ultra-Light Poly(N-isopropylacrylamide) Hydrogels: Light Weight Water Materials for Passive Thermal Management via Insulation and Cooling

The hydrogel achieves an ultra-light water-based structure (0.041 g cm −3 , 52.7 wt% water) by incorporating hollow foaming microspheres. Sealed air pockets enable ultra-low thermal conductivity (0.034–0.039 W m −1 K −1 ) and over 50 °C thermal shielding under high-temperature conditions. High solar reflectance (0.94) and infrared emittance (0.84) deliver up to 10.8 °C sub-ambient outdoor cooling.