HPMC‐Based Anisotropic Aerogels with HGM‐Alumina Fiber Co‐Filling for Extreme‐Temperature Thermal Management

ABSTRACT Overcoming the inherent density‐strength‐stability trade‐off in ceramic aerogels remains challenging. Herein, we present HAlCAs, an ultralight aerogel fabricated by integrating hollow glass microspheres and alumina microfibers within a nano‐hydroxypropyl methylcellulose (HPMC) matrix. Utilizing a sol‐gel process followed by directional freeze‐casting, we construct a deliberately engineered, 3D interwoven scaffold with uniformly dispersed fibers and microspheres. This unique “rigid‐yet‐flexible” architecture achieves a record porosity of 96% and an ultralow density of 20 mg cm −3 . Critically, it endows HAlCAs with fully recoverable superelasticity across an extreme temperature range (−196°C to 1200°C), while simultaneously suppressing structural collapse and thermal‐conductivity surges. The resultant aerogel exhibits exceptional thermal insulation, with a room‐temperature conductivity of 0.028 W m −1 K −1 that rises minimally to only 0.046 W m −1 K −1 even at 1200°C. Remarkably, a 20 mm‐thick HAlCAs sample reduces the backside temperature by 1000°C when exposed to a 1200°C flame, highlighting its outstanding flame barrier performance. This green, scalable process routinely yields monoliths from abundant, low‐cost precursors. Combining ultralow density, high temperature superelasticity, superior thermal insulation, and intrinsic flame retardancy. HAlCAs aerogels offer opportunities for next‐generation thermal super‐insulators in extreme environments, including hypersonic thermal‐protection systems, deep‐space insulation cabins, industrial furnaces, and battery packs.