I believe twisted quads are actually treated like a membrane - they really take on saddle shapes. In the renderer, not in preview.

On the previous page, MG pointed out (and I think it's true) that the cloth sim is just moving vertices with simulated springs and tensioners between them and in a strict sense triangulation doesn't have a lot to do with this.

However, in order to perform the vertex against polygon collision tests, particularly the OVACP, it has to consider the twisted shapes of the cloth polygons during the simulation. Does it treat them as triangles or as membranes? If triangles - which kind? Does it choose one diagonal or another, or does it test against BOTH triangulations? (That's what I'd do.) Or does it have some in-between thing it does with pretending that it's dealing with a membrane, but not with the high density that the renderer does?

Lots of questions.

Of course if you strictly model in triangles, all these questions are moot! You control everything and there should be no confusing poke throughs with OVACP.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)