Have been absent some; we are in the process of moving to Eagle CO and the process is overwhelming! My layout is still in my head, but I do have tacit approval from my wife; major achievement! Question is I read here about various types of sheet foam for carving landscape; pink, blue, white. Aside from the patriotic colors, what is the difference between them? I saw on one thread chunks of foam that didn't seem to carve very well; it crumbled. What are the materials? While I'm at it, what kind of knife seems to work best? Bread knife, serrated blade, or? I'm thinking in terms of at least 2" of foam under the trackbed and I figured I would lay that and carve it later to form hollows or small streams and the like. So I would want a knife that would cut cleanly.