Thanks Graham! That's a great idea. I'm going to try the following system: When colliding surfaces A and B mu, mu2: sqrt(A*B) slip1, slip2: sqrt(A*B) bounce, bounce_vel: average(A,B) motion1, motion2: average(A,B) softCFM, softERP: max(A,B) I'm really not sure about slip (FDS) and motion, since I've never used them before. -Alex