This has been mentioned before, but would it be feasible to make a wall that blocks wind and pressure like walls do, but permits particles to pass through?

I realize that single width walls permit some pressure through, I think. And I realize also that pressure and velocity tie in a lot torwards particle movement. I'm not sure if a wall that stops wind but not particles would be easy to pass through for particles.

I'm not sure how feasible this is. >_<

You'd be able to get away with some really trippy-looping things, too. @_@

The tricky thing is that, I'm wondering how Velocity and Pressure differ. I know that velocity is useful to moving elements, and so I'm wondering if blocking off velocity would simply stop anything from passing through.

It already exists. Just use Pipe element thick enough to act as a sponge/block to pressure, and the effect is 99% the same.