High Density Insulation Board or Insulation Foam Board is a staple of model train, village and gaming terrain builders. Stacked in layers it can be glued together to make hills and mountains. It is easily shaped with a wood shaver or a wood rasp file. The foam is available from Lumber yards (builders yards) usually in two by eight foot sheets. Foam thicknesses vary from 1/2 inch to 2 1/2 inches.
Common makers of extruded foam insulation include: Dow Corning (blue foam), Owens - Corning (pink foam), Amoco (green foam).
High density insulation board is not the same material as styrofoam, floral art foam etc.