Bacterial Cellulose‐Based Bilayer Passive Cooler for High‐Performance Radiative/Evaporative Cooling

Passive cooling material presents a zero‐energy solution to the rapidly increasing global demand for cooling. However, these materials face energy/resource‐intensive and pollution‐intensive manufacturing, posing significant challenges to scalability and long‐term energy‐saving applications. Here, biosynthesized bacterial cellulose (BC) with a 3D interconnect porous structure was employed as a versatile template to develop an BC‐based bilayer passive cooler. The cooler consists of a methyltrimethoxysilane‐modified hydrophobic BC (mBC) aerogel and a carboxymethyl cellulose‐reinforced hydrophilic BC (cBC) adsorptive material named mBC@cBC. This forms an asymmetric interfacial structure with a hydrophobic radiative layer and a hydrophilic evaporative layer. Owing to the synergistic coupling of radiative and evaporative cooling, the mBC@cBC cooler achieves a sub‐ambient temperature drop of 11.1°C on a clear day under 760 W·m −2 solar irradiation. Furthermore, it enables a remarkable temperature reduction exceeding 55°C on high‐temperature surfaces (80°C). The cooler is broadly applicable to low‐temperature storage, food preservation, and cold‐chain logistics. This work addresses the challenges of low‐carbon manufacturing and scalability in passive cooling materials and provides an innovative solution for sustainable and environmentally friendly cooling technologies.