The specific system and matrix realization shown in Fig. is employed here as a particularly strong illustration of the important role of the connectivity issues in the overall performance of the membrane. Indeed, the permeability across the whole structure shown in the figure hinges on a single passage or channel in the middle of the structure (shown in the ellipses in the figure). All molecules diffusing in the pressure gradient across this structure must pass through this channel. The local selectivity calculated for this crucial link is very close to the average overall perm-selectivity of the whole structure and it is much lower than the sorption selectivity for the same structure.