Foam comes in several densities (often color coded) with different compressive strengths from 10 psi to 60 psi. The higher strengths are used in construction and the lower as insulation. You won't find the former in the big box stores.
The lower strength foams will not hold screws. You must screw into some other substrate. like plywood. You can't screw the track to the foam. You'll need to glue the track to the foam which is not ideal.
Search the forum for "homasote" and "foam" in the layout construction threads. I thinl you'll find the answers to your questions.
Jan
