This PDF file includes:

• fig. S1. Photograph of the experimental setup.
• fig. S2. Diameter of TiO₂ fibers at different concentrations of PVP.
• fig. S3. Structural characterization of ZrO₂ nanofiber sponge.
• fig. S4. Structural characterization of YSZ nanofiber sponge.
• fig. S5. Structural characterization of BaTiO₃ nanofiber sponge.
• fig. S6. Room temperature compression and recovery of different ceramic nanofiber sponges.
• fig. S7. An Ashby plot of compressive modulus versus relative density to compare the present ceramic sponge with different foams and aerogels.
• fig. S8. In situ SEM cyclic compression of TiO₂ nanofiber sponge.
• fig. S9. Compressive testing of TiO₂ nanofiber sponge.
• fig. S10. Compression and recovery of ceramic nanofiber sponges heated with the flame of an alcohol lamp.
• fig. S11. Temperature distribution in the methane flame used in this work.
• fig. S12. Compressive stress-strain curves of YSZ nanofiber sponge at 400° and 600°C.
• fig. S13. XRD data of TiO2 calcined at 450°and 650°C.
• fig. S14. TEM images of TiO2 nanofibers after calcining at 650°C.
• fig. S15. Cyclic compressive stress-strain curves for 10 cycles of a TiO2 nanofiber sponge calcined at 650°C.
• fig. S16. Hydroscopicity of TiO₂ nanofiber sponge.
• fig. S17. A TiO₂ nanofiber sponge, which absorbed methylene blue solution was compressed and then recovered after being released.
• fig. S18. Temperature raising on the top surface of a ZrO₂ nanofiber sponge and other materials on a 400°C heating stage.
• table S1. The densities and thermal conductivities of ZrO₂ nanofiber sponge and other thermal insulation materials.
• References (35–46)

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Other Supplementary Material for this manuscript includes the following:

• movie S1 (.mp4 format). Room temperature compression and recovery of TiO₂, ZrO₂, and BaTiO₃ nanofiber sponges.
• movie S2 (.mp4 format). In situ SEM compressive testing of a TiO₂ nanofiber sponge.
• movie S3 (.mp4 format). Compressive testing of macroscopic TiO₂ nanofiber sponge for 100 cycles.
• movie S4 (.mp4 format). Compression of TiO₂, ZrO₂, and BaTiO₃ nanofiber sponges in an alcohol flame.
• movie S5 (.mp4 format). In situ SEM compressive of a TiO₂ nanofiber sponge at 400�C.
• movie S6 (.mp4 format). Compression and recovery of YSZ nanofiber sponge in a high-temperature methane flame.
• movie S7 (.mp4 format). YSZ nanofiber sponge maintaining elasticity after cyclic compression in the methane flame.

Download Movies S1 to S7