Lightweight and flexible thermal insulation materials have gradually become a research focus. In this work, the flexible YAG fibrous membrane which can be folded in half after heat treatment at 1200 °C for 2 h was prepared. The crystallization process, mechanical properties, and thermal insulation properties of the YAG fibrous membrane were studied. The as-prepared YAG fibrous membrane has no mesophase formation during the crystallization process, and its tensile strength was 2.43 MPa. The self-supporting effect of single fibers made YAG fibrous membrane had ultra-high porosity. Its density was 27.34 mg/cm3, which made it have thermal insulation performance comparable to aerogel. When the hot surface is 1200 °C, a 10 mm thick YAG fibrous membrane can stabilize the temperature of the cold surface at 320 °C. The YAG fibrous membrane is expected to be used as a new generation of lightweight, high strength, flexible, and high-efficiency thermal insulation materials for extremely high temperature conditions.
