The development of high-efficiency thermal insulation materials is crucial for terrestrial and space applications under extreme conditions. Synthetic aerogels, featuring porosities up to 99%, can reach the values of ~10 mW m ⁻¹ K ⁻¹ under vacuum. However, whether natural materials can achieve this performance remains an open question. Here, we report lunar agglutinates from the Chang’E-5 mission that exhibit thermal conductivities as low as ~8 mW m ^{− 1} K ^{− 1} under vacuum, surpassing most high-performance aerogel materials — at modest porosities of only 7–30%. Integrated structural characterizations and atomic-to-mesoscale simulations demonstrate that the space-weathering-forged multiscale voids and multiphase interfaces collaboratively suppress phonon transport within agglutinate particles, leading to their ultra-low thermal conductivities. These natural structures demonstrate a non-porosity-dominated thermal insulation mechanism. The findings redefine the microstructural design principles for super-insulating materials and provide a particle-scale explanation for the ultralow thermal conductivity of lunar regolith.

Under extreme conditions, including atomic scale, ultra-fast processes, and ultra-high power density, the continuous-medium hypothesis and local equilibrium approximation of classical transport theory no longer hold, with interface effects governing system behavior