The tunability or control of flexibility through crystal size engineering has now been established in many other framework materials, and affects different types of flexibility: gate opening, bistable materials, negative adsorption, etc. Bose et al. demonstrated the effect of crystal size and morphology on the adsorption-induced gate-opening of ZIF-7 (ZIF = Zeolitic Imidazolate Framework). While crystals of ZIF-7 of all sizes exhibit some flexibility, the gate opening and closing pressures for CO 2 adsorption can be modulated, as well as the abruptness of the transition (indicated in the slope of the isotherm step).