One of its remarkable characteristics is the possibility to access two distinct phases by ad-or desorbing guests into/from the structure. After synthesis, the structure is in a solvent-filled open pore state (denoted op). Upon solvent removal, it can collapse (unit cell volume changes to less than half the initial volume) into a closed pore state (denoted cp). This collapse is, however, not observed if the synthesized crystals are smaller than a certain threshold (approximately 500 nm in length). The size dependence of the flexibility is not a unique characteristic of DUT-8(Ni) and has been observed and studied in other materials. Another important factor for the flexibility of DUT-8(Ni) is the exact conformation of the material. As shown previously, the nonlinearity of the ndc linkers give raise to conformational isomerism. We showed that certain conformers result in a specific stacking of the ndc linkers in the cp phase, increasing the dispersion interactions and therefore stabilizing it with respect to the op phase.