There's a fun experiment where you can grease a kitchen strainer and if the holes are small enough it'll hold water because of the surface tension.

And at the same time it will pass a thick oil... all due to surface tension, polarity, etc.

Which is to say don't think about the filter as a geometrical sieve that has holes that pass molecules solely based on their size (either it fits or not).

This is not true even at macro level.

Your plumbing is leak-tight, but it's not water vapor-tight.

plumbing is not water vapor tight?

Plumbing for gaz and water follow different norms and pursue different sealing strategy. This distinction is omnipresent in gasket and screw thread engineering.

At the molecular level, nobody cares about your intuition.

so true