I have finally, after many years, made the conversion from polystyrene as my main source of building material to high density extruded foam. It comes in various colours, pink, blue or yellow but all have the similar virtues of strength, allowing score-and-snap cutting and also enabling the paitient modeller to emboss detail with a scribing tool.
The material is relatively expensive, so I've decided that I ought to prototype my building projects in white polystyrene to settle questions of technique before applying hot wire cutter to my more expensive building material.
What you are seeing here is my first experiment; a Crusader donjon from Northern Palestine (the plain of Sharon, no less) around about 1120-30CE.
The knights and infantry are all Spencer Smith "Classic" Normans. Excellent figures which I am enjoying painting very much at the moment. There is a deal of pose-ability and even some conversion potential that is quite appealing to me.