As global temperatures rise and extreme heat events become increasingly frequent, the energy required to keep indoor spaces comfortable is surging 1.Building cooling alone accounts for roughly 15% of the world's primary energy consumption, driving substantial greenhouse gas emissions 2.Conventional mechanical cooling systems-though effective-come with high energy and carbon costs.This urgent context has propelled the search for sustainable, low-energy cooling strategies 3.Passive daytime radiative cooling (PDRC) has emerged as one of the most promising solutions.By reflecting incoming solar radiation and emitting mid-infrared (MIR) thermal radiation through the atmospheric window (8-13 m), PDRC materials can cool surfaces below ambient temperature without external energy input 4.Yet, despite remarkable advances in optical engineering, most PDRC materials deliver cooling powers below 150 W m -2 -insufficient for many real-world needs, especially under strong solar irradiance 5.Moreover, the practically attainable cooling performance is often further reduced by weatherdependent factors such as atmospheric humidity, cloud coverage, aerosol loading, and environmental thermal disturbances, which collectively suppress the effective radiative window and introduce additional nonradiative heat gains.Hu et al. 's study 6, recently published in Advanced Materials, broke this long-standing performance barrier.By integrating radiative cooling with phase-change thermal regulation in a bioinspired hierarchical composite, the authors report a record cooling power of 226 W m -2 and an average subambient temperature reduction of 10.1 C.Their nacre-pearl-inspired architecture represents a conceptual leap forward in the design of hybrid passive cooling systems.The fundamental challenge in developing high-performance radiative-phase change hybrid cooling (RPHC) materials lies in reconciling competing functional requirements 7,8.On one hand, strong solar reflectivity and MIR emissivity demand a porous structure and high refractive index contrast 9.On the other hand, efficient phase-change heat storage requires high loading of phase change materials (PCMs), which often possess low reflectivity and tend to compromise porosity.Integrating PCMs can also introduce leakage, reduce structural stability, or create thermal barriers that limit heat transfer 10.Previous RPHC designs typically combined separate radiative and PCM layers, but the weak interfacial thermal coupling limited performance.Homogeneous composites, in contrast, improved thermal contact but
Lu et al. (Mon,) studied this question.