The recent decade has witnessed the booming development of framework materials, such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs). Unlike their conventional counterparts (e.g., silica, activated carbon, zeolite), MOFs/COFs have crystalline structures, uniform yet tunable pore size, and versatile chemical compositions suitable as adsorbent materials and membrane materials for storage and separation applications. In this talk, I will introduce our group’s studies on the application of flexible framework materials for gas storage and separation. We have synthesized a series of flexible and stable MIL-53(Al) type MOFs. Their breathing behavior under high pressures of CH₄ can be controlled by the systematic installation of hydrogen bonding sites into the frameworks. Such control has been fine-tuned to induce high deliverable capacities of CH₄ in MOFs by changing pressure, temperature, density, and even synthetic conditions. We have also fabricated ultrathin 2D MOF membranes using exfoliated MOF nanosheets. Because of the flexibility of the MOF nanosheets, those membranes exhibit responsive gas separation behaviors under the stimuli of temperature or pressure, paving the way for the rational design of smart membranes for H₂ purification and CO₂ capture.