Thermal insulation under extreme conditions requires materials that can withstand complex thermomechanical stress and retain excellent thermal insulation properties at temperatures exceeding 1,000 degrees Celsius1–3. Ceramic aerogels are attractive thermal insulating materials; however, at very high temperatures, they often show considerably increased thermal conductivity and limited thermomechanical stability that can lead to catastrophic failure4–6. Here we report a multiscale design of hypocrystalline zircon nanofibrous aerogels with a zig-zag architecture that leads to exceptional thermomechanical stability and ultralow thermal conductivity at high temperatures. The aerogels show a near-zero Poisson’s ratio (3.3 × 10−4) and a near-zero thermal expansion coefficient (1.2 × 10−7 per degree Celsius), which ensures excellent structural flexibility and thermomechanical properties. They show high thermal stability with ultralow strength degradation (less than 1 per cent) after sharp thermal shocks, and a high working temperature (up to 1,300 degrees Celsius). By deliberately entrapping residue carbon species in the constituent hypocrystalline zircon fibres, we substantially reduce the thermal radiation heat transfer and achieve one of the lowest high-temperature thermal conductivities among ceramic aerogels so far—104 milliwatts per metre per kelvin at 1,000 degrees Celsius. The combined thermomechanical and thermal insulating properties offer an attractive material system for robust thermal insulation under extreme conditions.

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Porous carbon materials have exhibited many superior characteristics with extensive applications. To adequately exert their advantages at macroscale, the mechanical property plays a critical role to ensure the structural stability and functionality. Porous carbon monoliths overcome brittleness by endowing compressive superelasticity but are still plagued by poor toughness, easily suffering from the tensile, bending, or torsional fracture. Here, inspired by the biostructure of succulent plants, graphene aerogel is used to mimic the hydrenchyma tissue, carbon nanotube aerogel film as the epidermis, and graphene oxide ethanol solution as the hemicellulose binder to make ultraflexible carbon aerogels (UCAGs), addressing the critical and bottleneck issue between mechanics and functionality. The UCAGs feature a sequence of robust mechanical properties simultaneously, including compressive strain up to 99.5%, tensile strength up to 460 kPa, bending and torsional angle up to 180°. This ultraflexible aerogel is exploited for large‐deformable, and high‐sensitive strain sensor with extended working temperature (−196 to 400 °C), as well as lightweight thermal regulator with record‐high switch ratio (500:1). The high‐performance structures of this type establish a set of fundamental considerations in structural design of inorganic aerogels for a wide spectrum of applications.

Thermal sealing is essential to prevent thermal runaway in aerospace and mechanical fields. Ceramic aerogels are attractive candidates but often show limited thermomechanical performance and thermal radiation opacification that may...