Dimitris Wrote: For example: if such a friction attribute exists and for wood it is u1 and for steel u2 then the friction coefficients for wood-wood, wood- steel, steel-steel should be f(u1, u1), f(u2, u2), f(u3, u3) respectively, where f is some function. I've been searching all over the web for something like that but to no avail. I am not surprised. Ander