There is a company I found showing at Historicon in 2007 called Precision Products (http://www.appliedimaginationinc.com/), that manufactures vacuum formed polystyrene sheets of terrain - I have been working on their rivers in one of my projects - and embossed sheet for model building. Things like brick and flagstone and such for the exterior of models.
They also manufacture something similar to foamcore, but with a thin styrene exterior rather than the more common (dare I say 'traditional'?) paper exterior sandwiching the foam.
Has anyone used this material? It sounds rather more sturdy than regular foamcore, what with being more water-resistant, and the fact that I tend to use water-based glues and paints makes this a definite plus.
Anyone have practical experience of the stuff? Leave a comment if you do!