Carbon Nanostructure–Enabled High‐Performance Thermal Insulation for Extreme‐Temperature Application

High‐temperature thermal insulation materials (TIMs) are critical for thermal protection and management systems, where reduced thickness combined with superior insulating performance is highly desirable. This study reports a class of stacked films composed of super‐aligned carbon nanotubes (SACNT‐SF) that exhibit ultralow thermal conductivity across a wide temperature range. In vacuum, SACNT‐SF achieves an effective thermal conductivity of 0.004 W m −1 K −1 at room temperature and 0.03 W m −1 K −1 at 2600 °C. The exceptional insulating performance arises from the intrinsic properties of SACNT‐SF, including nanometer‐scale tube diameters, a highly anisotropic and nanoporous structure, ultralow density, and the high extinction coefficient of sp 2 carbon. These attributes effectively suppress heat transfer via solid conduction, gas conduction, and thermal radiation. Additionally, SACNT‐SF is nanometer‐thick and mechanically flexible, allowing conformal integration onto surfaces with complex geometries. These characteristics make SACNT‐SF a strong candidate for next‐generation thermal insulation in extreme environments.