The results presented in Tab. 2 give us an opportunity to discuss broadly the challenges associated with attempts to quantitatively reproduce the experimental behavior. The most significant issues are associated with the forcefield parameters and high degree of scattering in individual molecular simulation trajectories. Forcefield parameters govern polymer dynamics and fluctuations of the size of the cages and transient windows between them. In our work, the DRIEDING forcefield is employed. This a generic forcefield and is not specifically parameterized for studying fluid transport in polymeric membranes. While more specialized forcefields exist, accurate representation of the cage dynamics in polymers remains difficult.