I've looked through the list of walls and can't find anything like this. Am I missing something? Is there some technical reason this can't be done? It seems like the kind of thing that would be there.
actually, this doesn't exist. I'm not really sure why though. I think it should be added, but I remember some reasons against it I think, maybe i'll ask simon. (it's sort of possible with TTAN with a tmp of 1 right now)
It is hard to implement because particle movement relies on the air (pressure) simulator. blocking one would set the movement of the other to 0 (or in some cases not applicable). @jacob1 your a dev! you should know this!