Membranes and barriers are used all the time in industrial and lab settings, and you may even have a few of them around the home. They can help keep materials apart that need to be separated, or can selectively allow certain materials to mix while holding others back. Graphene, the two-dimensional hexagonal lattice of carbon, is thought to be completely impermeable to all gases and liquids. That would obviously make it an extremely effective barrier film.
Initial experiments with gases such as helium, hydrogen, nitrogen, and argon found that almost no gas was able to move across the membrane over a period of a few days. Calculations on these results yielded a helium permeation rate below 10-12 g/cm2*s*bar, consistent with values reported elsewhere for pure graphene films—basically no gas was getting through. Computing the bulk permeability of the material gave a value of approximately 10-15mm*g/cm2*s*bar. Put into more useful terms, this means that less gas will seep through a submicron thick GO film than would pass through a 1 mm thick glass barrier in an equivalent amount of time!
Carrying out a similar experiment with common liquids (ethanol, hexane, acetone, decane, and propanol) revealed that no weight loss could be detected after several days of the fluid resting on the membrane. This set an upper limit on liquid bulk permeability of 10-11 mm*g/cm2*s*bar. However, something unexpected happened when they repeated the test with water. There was a huge weight and the evaporation rate was nearly the same as though there was no membrane or barrier in place.
After this unexpected result, the authors repeated the test with helium to ensure that no physical damage had occurred to the membrane; no helium leakage was observed. In fact, it was only when the membrane was a couple of microns thick that any resistance to the flow of water was observed. Computing the bulk permeability of water gave a result of 10-5 mm*g/cm2*s*bar, a value 1010 (10,000,000,000) times greater than that for helium. This membrane was essentially impermeable to a small, inert gas, but allowed water to freely move through it.