Elastic ceramics: Aerogels hold promise as lightweight replacements for thermal insulation. However, poor mechanical stability has hampered progress in moving toward commercialization. Xu et al. designed a mechanical metamaterial that pinches in a small amount when you compress it (see the Perspective by Chhowalla and Jariwala). This is characteristic of materials with a negative Poisson's ratio and dramatically improves mechanical stability. The trick was using three-dimensional graphene structures to template the ceramic aerogels, thus producing a superinsulating material endowed with excellent mechanical properties. Science , this issue p. 723 ; see also p. 694

Thermal conductivity is a crucial material property for a diverse range of energy technologies, ranging from thermal management of high power electronics to thermal insulation for building envelopes. This review discusses recent advances in achieving high and low thermal conductivity ( k ) as relevant for energy applications, from high- k heat spreaders to low- k insulation. We begin with a brief introduction to the physics of heat conduction from both theoretical and computational perspectives. The heart of the review is a survey of recent advances in high- and low- k materials. The discussion of good heat conductors for thermal management includes inorganics and polymers in both bulk and low dimensional forms. For insulators, the discussion covers the effects of chemical composition, crystal structure, and defects and porosity. Promising areas for future research in both fundamental materials science and engineering technologies are noted.

Inorganic aerogels have exhibited many superior characteristics with extensive applications, but are still plagued by a nearly century-old tradeoff between their mechanical and thermal properties. When reducing thermal conductivity by ultralow density, inorganic aerogels generally suffer from large fragility due to their brittle nature or weak joint crosslinking, while enhancing the mechanical robustness by material design and structural engineering, they easily sacrifice thermal insulation and stability. Here, we report a chemically bonded multi-nanolayer design and synthesis of a graphene/amorphous boron nitride aerogel to address this typical tradeoff to further enhance mechanical and thermal properties. Attributed to the chemically bonded interface and coupled toughening effect, our aerogels display a low density of 0.8 mg cm⁻³ with ultrahigh flexibility (elastic compressive strain up to 99% and bending strain up to 90%), and exceptional thermostability (strength degradation <3% after sharp thermal shocks), as well as the lowest thermal conductivities in a vacuum (only 1.57 mW m⁻¹ K⁻¹ at room temperature and 10.39 mW m⁻¹ K⁻¹ at 500°C) among solid materials to date. This unique combination of mechanical and thermal properties offers an attractive material system for thermal superinsulation at extreme conditions.