Captain Cardboard, yes; Circuitboard, no.
It seems from the rest of the responses no one here knows what foamcore is, since they are all offering sculpting tools of some form or another as the solution.
Foamcore comes in varying thicknesses, starting at 1/8 of an inch, up to 1/2 inch. Typically, 3/16 is used as it is nearly 1/4 inch thick and is strong enough for most uses. The material looks like thick, white cardstock, but it is actually two sheets of sturdy cardstock with a 'foam core' between them. This foam has a styrene base as all sorts of chemicals and paints will eat into it, but it is rather spongy by nature, but not beaded.
Other materials in the same family (clad foam core) are Gatorboard and Artcore. Gatorboard is a very interesting material in that the outside surface is very similar to Masonite, but very thin. The core, in this case, is very different in that the foam is hard and brittle. Gatorboard is more expensive, but much more durable than Foamcore, which will show dents easily.
Artcore is identical to Foamcore except the outside cladding is styrene plastic, rather than heavy cardstock. This is the least durable of the 3, but you can glue it together with solvent type cements, though they have to be used sparingly as the plastic surface is rather thin.
Scott snipped-for-privacy@AOL.com