I started to write what you wrote a couple times, but I despaired of having to type all that. Thank you.

Meanwhile, I have found the same. The forces don't make sense with respect to the real world. And - rotation occurs spontaeously for no reason, because some vertices experience critical force and go from static to dynamic friction, while other vertices remain static. At random times, one part will happen to have more stuck vertices than the other, creating a torque. Once rotation sets in, inertia keeps it going.

High stretch resistance tends to make it less likely for a vertex to start moving while its neighbors are still stationary. But it's still so unpredictable that I'm not sure anything useful comes out of it, especially if extremely high resistance is required and ends up cause the cloth to behave like cardboard.

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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)