Question

Imagine this: you are on the job site doing an inspection. You’ve specified rigid polyisocyanurate insulation board against the foundation. The board has been installed and the area backfilled. All you can see is the tan-colored edge of the board. You think that the contractor installed extruded polystyrene. The contractor swears she used the correct product. You have her dig down to expose the face label. Who is right?

Answer

You owe the contractor an apology and perhaps a beer. The edge color of extruded polystyrene is typically pale blue, green, or pink. If it is white you can expect to find expanded polystyrene, if pale gold/tan, polyisocyanurate.