How do 2 Physics Material 2D Interact with Each other?

Specifically the bounce and friction combines.

For example the 3D Physic Material has a Friction Combine, and a Bounce Combine property to it which you can select how the materials interact with each other.

    Average	The two friction values are averaged.
    Minimum	The smallest of the two values is used.
    Maximum	The largest of the two values is used.
    Multiply	The friction values are multiplied with each other.

Yet Physics Material 2D do not have these properties. I would figure it to be one of these, but it isn’t documented anywhere. :confused:
My guess after minimal testing is that it uses the maximum of the 2, but I really have no clue.

I think the values are multiplied by default.

I have added the friction values of the object and ground to the animation. As you can see, because 0.2 * 1 == 2 * 0.1 (the leftmost setups). Additionally, values of 0 and 1000 make the object slide, but a missing Physics Material (x) is treated differently.

alt text

From here:

friction = sqrtf(shape1->friction * shape2->friction)