Synergistic Enhancement of Optical and Mechanical Properties in Polydimethylsiloxane via Microcrystalline Cellulose/ SiO ₂ Photonic Structure for High‐Efficiency Flexible Radiative Cooling

Passive radiative cooling, as a zero‐energy, environmentally friendly refrigeration technology, holds significant application potential in mitigating global warming and related fields. However, a critical bottleneck persists: the inherent trade‐off between its optical cooling performance and mechanical robustness, which severely limits its practical deployment. This paper proposes a one‐pot ball milling process that simultaneously refines, mixes, and chemically fuses microcrystalline cellulose (MCC) and silica (SiO 2 ) to fabricate hierarchical MCC/SiO 2 hybrid particles. The engineered fillers are then seamlessly integrated into a polydimethylsiloxane (PDMS) matrix, ultimately yielding flexible, mechanically robust, and highly efficient radiative cooling composite MCC/SiO 2 /PDMS film for synergistic enhancement of optical and mechanical properties. The optimized film exhibits a record‐high solar reflectance of 94.58% and a long‐wave infrared emissivity of 95.22%. Notably, it breaks the traditional performance trade‐off: the incorporation of MCC/SiO 2 enhances the mechanical strength and toughness of PDMS by 1.6 MPa and 1.02 MJ cm −3 . Outdoor tests demonstrate an average sub‐ambient cooling effect of 8°C under direct sunlight. This work provides a novel paradigm for designing sustainable high‐performance materials through microstructural engineering of hybrid fillers.