While it has long been known that some highly adsorbing microporous materials suddenly become inaccessible to guest molecules below certain temperatures, previous attempts to explain this phenomenon have failed. Here we show that this anomalous sorption behaviour is a temperature-regulated guest admission process, where the pore-keeping group’s thermal fluctuations are influenced by interactions with guest molecules. A physical model is presented to explain the atomic-level chemistry and structure of these thermally regulated micropores, which is crucial to systematic engineering of new functional materials such as tunable molecular sieves, gated membranes and controlled-release nanocontainers. The model was validated experimentally with H2, N2, Ar and CH4 on three classes of microporous materials: trapdoor zeolites, supramolecular host calixarenes and metal-organic frameworks. We demonstrate how temperature can be exploited to achieve appreciable hydrogen and methane storage in such materials without sustained pressure. These findings also open new avenues for gas sensing and isotope separation.

K-CHA_273 K_rhombohedralCrystallographic Information File (CIF) file of K-CHA in rhombohedral structure at 273 KK-CHA_273K_cubicCrystallographic Information File (CIF) of K-CHA in cubic structure at 273 KKCHA2.2_supercell_GCMC_cubicCrystallographic Information File (CIF) for a potassium exchange chabazite with a Si/Al ratio of 2.2, in a 3 x 3 x 3 supercell for GCMC calculations, in cubic structure.KCHA2.2_supercell_for_GCMC.CIF