The foam is easily cut with a Stanley-type utility knife. The knife will make very clean cuts with a bit of practice. A hack-saw blade (with a handle preferably) is also very useful. The foam can be shaped (rounded, beveled, etc.) with a Stanley Surform tool. Elmer's white glue is very good for gluing the foam to wood, foam to foam, foam to cork (roadbed) and also for attaching the track to the roadbed. Use plenty of "T" pins to hold things in place while the glue dries.
Note: I highly recommend that you use only extruded Styrofoam which is usually blue or pink. I started with the beaded white foam before I realized that the extruded foam was so much superior in strength and texture and so much easier to cut and form. You will notice that I left some of the white foam in place since it was cemented to the plywood and would be covered with blue foam or plaster. I did use some 2" thick white foam for some of the "risers" on the upper loop. This worked OK but 2" blue foam or the 1/2" blue foam would have worked better. So, to sum it up, in case there are any doubts on my position, don't use the white stuff!
Many folks were using foam for layouts and that seemed like a good idea. I couldn't find any 2" thick foam so it occurred to me to use 1/2" blue Styrofoam with the "cookie cutter" method similar the long used plywood method. Here you can see some of the foam sub-roadbed cut and supported with other pieces of foam. You can see some white beaded foam but I would strongly advise that only the blue extruded foam be used. The extruded foam is much stronger, finer grained and easier to cut and work with. Don't use the white stuff! (See Note below.)
The 1/2" foam superstructure gets its strength from the "box girder" effect of the construction. The center photo and the photo to the right below show a good examples of this "box" effect. The cookie cutter sub-roadbed is supported by vertical "walls" of the 1/2" foam which are glued to the foam base sheet and, of course, to the sub-roadbed forming a very strong box-like structure. Even though the riser wall sections may be cut in short lengths to make cutting and fitting easier the sub-roadbed and base sheets are mostly monolithic. The resulting structure has many of the qualities of box, "T", "L" and "I" beam girders making the overall "superstructure" very rigid and strong.
