ZIF-8 is a flexible zeolitic imidazole-based metal–organic framework whose narrow pore apertures swing open by reorientation of imidazolate linkers and expand when probed with guest molecules. This work reports on the crystal size dependency of both structural transitions induced by N₂ and Ar adsorption and dynamic adsorption behavior of n-butanol using well-engineered ZIF-8 crystals with identical surface area and micropore volume. It is found that the crystal downsizing of ZIF-8 regulates the structural flexibility in equilibrium adsorption and desorption of N₂ and Ar. Adsorption kinetics of n-butanol in ZIF-8 are strongly affected by the crystal size, however, not according to a classical intracrystalline diffusion mechanism. Our results suggest that structural transitions and transport properties are dominated by crystal surface effects. Crystal downsizing increases the importance of such surface barriers.