Whiteness arises from diffuse and broadband reflection of light typically achieved through optical scattering in randomly structured media. In contrast to structural colour due to coherent scattering, white appearance generally requires a relatively thick system comprising randomly positioned high refractive-index scattering centres. Here, we show that the exceptionally bright white appearance of Cyphochilus and Lepidiota stigma beetles arises from a remarkably optimised anisotropy of intra-scale chitin networks, which act as a dense scattering media. Using time-resolved measurements, we show that light propagating in the scales of the beetles undergoes pronounced multiple scattering that is associated with the lowest transport mean free path reported to date for low-refractive-index systems. Our light transport investigation unveil high level of optimisation that achieves high-brightness white in a thin low-mass-per-unit-area anisotropic disordered nanostructure.

The extremely brilliant whiteness shown by the Cyphochilus beetle is generated by multiple scattering of light inside the ultrathin scales that cover its body, whose interior is characterized by an anisotropic nanostructured network of chitin filaments. It is demonstrated that the structural anisotropy of the network is crucial in order to achieve high broadband reflectance from such a thin, low‐refractive‐index system.

Energy-saving cooling materials with strong operability are desirable for sustainable thermal management. Inspired by the cooperative thermo-optical effect in the fur of a polar bear, we develop a flexible, superhydrophobic, and reusable cooling "skin" by laminating a poly(dimethylsiloxane) film with a highly scattering polyethylene aerogel. Owing to its high porosity (97.9%) and tailored pore size of 3.8 ± 1.4 μm, it can achieve superior solar reflectance (R̅ sun ∼ 0.96) and high transparency to irradiated thermal energy (τ ̅ PE,MIR ∼ 0.8) at a thickness of 2.7 mm. Combined with the low thermal conductivity (0.032 W m −1 K −1 ) of the aerogel, the cooling skin exerts midday sub-ambient temperature drops of 5−6 °C in a metropolitan environment, with an estimated limit of 14 °C under ideal service conditions. Our generalized bilayer approach can be easily applied to different types of emitters, bridging the gap between night-time and daytime radiative cooling and paving the way for more cost-effective and scalable cooling materials.

CELES is a freely available MATLAB toolbox to simulate light scattering by many spherical particles. Aiming at high computational performance, CELES leverages block-diagonal preconditioning, a lookuptable approach to evaluate costly functions and massively parallel execution on NVIDIA graphics processing units using the CUDA computing platform. The combination of these techniques allows to efficiently address large electrodynamic problems (>10 4 scatterers) on inexpensive consumer hardware. In this paper, we validate near-and far-field distributions against the well-established multi-sphere T -matrix (MSTM) code and discuss the convergence behavior for ensembles of different sizes, including an exemplary system comprising 10 5 particles.