Disclosed are gas cylinder assemblies for containing pressurized gas. The gas cylinder assembly has a polymeric liner and a low-permeability barrier layer. The polymeric liner a first end portion, a second end portion and a central body. The central body comprises an outer surface and an inner surface disposed between the first end and the second end. The gas cylinder assembly comprises a reinforcement structure wound over the central body. The gas cylinder assembly further comprises a metal foil interposed between the reinforcement structure and central body. The metal foil is configured to reduce permeation of contents of the polymeric liner.