Hierarchical Porous Mullite Fiber‐Based Ceramics With Excellent Thermal Insulation and Mechanical Properties

Mullite fiber‐based porous ceramics have exhibited promising potential for high‐temperature insulation applications due to their superior inherent thermal stability. However, achieving high porosity, high mechanical strength, and excellent thermal insulation properties simultaneously remains challenging for such materials. Herein, a hierarchical structure was designed by integrating a rigid three‐dimensional mullite fiber skeleton with an in situ formed honeycomb‐like nanopore network via glucose/NH 4 Cl synergistic foaming, realizing enhanced comprehensive performance. NH 4 Cl acted as a blowing agent to generate bubbles in situ, while glucose served as a carbon template, forming a polymer network through a derivatization reaction to stabilize the bubbles. The effects of sintering temperature and glucose/NH 4 Cl molar ratio on microstructure, mechanical properties, and thermal stability were investigated. The results showed that optimal samples sintered at 1200°C with a glucose/NH 4 Cl molar ratio of 1:3 exhibited 90.20% porosity, 0.316 g/cm 3 density, 0.48 MPa compressive strength, 0.0539 W/(m K) room‐temperature thermal conductivity, and 244.5°C backside temperature under 1200°C flame. This hierarchical structure improves deformation resistance and inhibits heat transfer, providing a scalable strategy for high‐performance lightweight thermal insulation materials.