gas seperation/barrier

[floosh]

any plastics that are permeable to water vapor but impermeable to larger gas molecules (50-150 m.w.)??

 

[gambro]

Yes. Several plastics are much more permeable towards water vapor than towards N2, O2 or CO2. Examples are plasticized PVC or PVF. The material with the highest water vapor permeability but a very low permeability towards other gasses, though, would be PA6. Please note that PA66 and other polyamides have a much lower water vapor permeability so you must use PA6.