Closed cell polystyrene,  can be blade cut, sanded, impressed, embossed, hot wire cut, die cut, sprayed with paint to dissolve in unique patterns you name it.  I have been using this material for 12 years making terrain for war gaming and train layouts and am always impressed with its versatility. This is the thickness that I use on all my buildings for walls, floors and roads.  Multi item auction buy as many as you wish with 1 shipping price anywhere in the US.

Sheets will be slightly more than 12x12 inch in size and approx 5/16 inch thick with variance of +- 0.05 inch