Flexibility in gas absorption Soft materials such as porous coordination polymer (PCP) can exhibit temperature-dependent flexible motions of their internal pores that can assist in gas separation and storage. Gu et al. designed a copper-based PCP with a ligand that contains phenothiazine-5,5-dioxide. The entrances to the porous cages changed size with temperature, when these functional groups underwent flipping motions. The change in gate size could lead to high selectivity for gas absorption and enabled the separation of oxygen from argon and of ethylene from ethane as well as long-term gas storage under ambient conditions. Science , this issue p. 387