Temperature is a fundamental parameter for all forms of lives. Natural evolution has resulted in organisms which have excellent thermoregulation capabilities in extreme climates. Bioinspired materials that mimic biological solution for thermoregulation have proven promising for passive radiative cooling. However, scalable production of artificial photonic radiators with complex structures, outstanding properties, high throughput, and low cost is still challenging. Herein, we design and demonstrate biologically inspired photonic materials for passive radiative cooling, after discovery of longicorn beetles’ excellent thermoregulatory function with their dual-scale fluffs. The natural fluffs exhibit a finely structured triangular cross-section with two thermoregulatory effects which effectively reflects sunlight and emits thermal radiation, thereby decreasing the beetles’ body temperature. Inspired by the finding, a photonic film consisting of a micropyramid-arrayed polymer matrix with random ceramic particles is fabricated with high throughput. The film reflects ∼95% of solar irradiance and exhibits an infrared emissivity >0.96. The effective cooling power is found to be ∼90.8 W⋅m−2and a temperature decrease of up to 5.1 °C is recorded under direct sunlight. Additionally, the film exhibits hydrophobicity, superior flexibility, and strong mechanical strength, which is promising for thermal management in various electronic devices and wearable products. Our work paves the way for designing and fabrication of high-performance thermal regulation materials.

Nanostructures on bodies of biological inhabitants in severe environments can exhibit excellent thermoregulation, which provide inspirations for artificial radiative cooling materials. However, achieving both large‐scale manufacturing and flexible form‐compatibility to various applications needs remains as a formidable challenge. Here a biomimetic strategy is adopted to design a thermal photonic composite inspired by the previously unexplored golden cicada's evolutionarily optimized thermoregulatory ability. A microimprint combined with phase separation method is developed for fabricating a biomimetic photonic material made of porous polymer–ceramic composite profiled in microhumps. The composite demonstrates high solar reflectance (97.6%) and infrared emissivity (95.5%) in atmospheric window, which results in a cooling power of 78 W m−2 and a maximum subambient temperature drop of 6.6 °C at noon. Moreover, the technique facilitates multiform manufacturing of the composites beyond films, as demonstrated by additive printing into general 3D structures. This work offers biomimetic approach for developing high‐performance thermal regulation materials and devices.

perpendicularly to the cellulose fibers, and 1.596 along with the fibers), hemicellulose (1.532), and lignin (1.61). [3] While holocellulose (cellulose and hemicellulose) is optically colorless, lignin is the main source of absorption (about 80-95% of wood light absorption) in the visible range. [10] Thus, lignin removing [11] or deactivating the chromophores inside lignin is required to make wood transparent. [12] Although major part of lignin is removed during chemical modification, some residual amount (1-3%) still remains in the wood [11] introducing minor absorption. A delignified wood (Figure 1a) is not yet transparent due to strong scattering of light, which occurs on the interfaces between the material structural components and air-filled voids between/within them. To minimize such scattering, the delignified template is infiltrated with a polymer of refractive index approximately matching the wood compounds. In several previous studies, polymerized methyl methacrylate (PMMA) whose refractive index is close to the average refractive index of delignified wood template (≈1.53) [11] was implemented. However, there always exists minor refractive index mismatch between the wood components and infiltrated polymer that leads to the light scattering. Moreover, as a consequence of mesoporous hierarchical structure of a wood template [13] with feature sizes scaling from micrometers-cellulose fibers, vessels, rays [14] (schematically presented in Figure 1b) down to nanometers (nanofibrils), [1,15] polymer infiltration process is not perfect, e.g., due to surface compatibility issues. This leads to formation of structural air-filled voids in the walls of the cellulose fibers consisting of nanofibrils (Figure 1c). It should be noted that additional airfilled voids can also be created via polymer shrinkage during polymerization [16] (Figure 1c). Hence, scattering in TW is caused by several factors: minor mismatch of the refractive indices between the delignified wood template and infiltrated polymer, multiscale porous hierarchical structure of the wood consisting of macro-, meso-, and nanopores, and presence of air-filled voids. Thus, despite relatively high optical transmittance, TW is, in fact, an optically anisotropic scattering medium.Traditionally optical properties of TW have been characterized via measuring the light total hemispherical luminous transmittance (referred as transmittance in the literature about TW) and haze. [11,17] While transmittance describes optical losses of a material, i.e., the fraction of the optical energy flux passing Transparent wood (TW) is a biocomposite material with hierarchical structure, which exhibits high optical transmittance and anisotropic light scattering. Here, the relation between anisotropic scattering and the internal structure of transparent wood is experimentally studied and the dependence of scattering anisotropy on material thickness, which characterizes the fraction of ballistic photons in the propagating light, is shown. The limitations of the conventional haze, as...

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Lytic polysaccharide monooxygenase (LPMO)-catalysed oxidation of cellulose has emerged as a green alternative to chemical modifications in the production of cellulose nanofibrils (CNFs) from wood pulp fibres. The effect of...