Aerogels with ultra-low thermal conductivity: Structural design, processing and applications

Aerogels can achieve thermal conductivities below that of static air, positioning them as promising lightweight thermal insulation materials for diverse service conditions. This exceptional thermal insulation performance stems from the simultaneous suppression of solid conduction (λ_s), gas conduction (λ_g), and radiative heat transfer (λ_rad) by their intricate nanoporous architectures. This review systematically summarizes recent advances in ultra-low thermal conductivity aerogels from the perspectives of heat transfer mechanisms, multiscale structural design, and fabrication strategies, and representative applications. We elucidate how microstructural characteristics—including pore size distribution, skeleton dimensions and orientation, and hierarchical porosity—govern macroscopic heat transport behavior, and discuss the underlying physical mechanisms, namely phonon scattering, the Knudsen effect, and radiative extinction, that collectively inhibit thermal conduction. From a structural design standpoint, we critically evaluate strategies such as particle–fiber networks, layered anisotropic frameworks, and hierarchical porous systems as representative approaches to balancing thermal insulation performance with mechanical stability. Regarding fabrication, we systematically review key technologies, with particular emphasis on sol–gel processing and various drying methodologies, outlining their progress and remaining challenges in enabling precise microstructural control and scalable production. Furthermore, we comprehensively survey the current deployment of these materials across critical domains, including building energy efficiency, energy storage, aerospace thermal protection, and personal thermal management. Finally, we identify key scientific and technological challenges and propose future research directions, aiming to inform both fundamental investigations and practical applications of ultra-low thermal conductivity aerogels.