Nature Materials, Published online: 19 November 2025; doi:10.1038/s41563-025-02424-2An organic crystal containing open channels and discrete voids responds to CO2 gas pressure by reversibly elongating along a single crystal axis. Although the voids initially appear too small to host CO2, structural flexibility permits gradual gas penetration and void expansion, triggering a cascading deformation that amplifies macroscopically.