I talked with my brother about the different types or foam board.

The non-faced insulation boards, colored pink, blue, or green, are extruded
polystyrene. Because of the nature of the extrusion process the boards have
enough structural strength to be handled, cut, and installed without any
additional coverings. (The color tells you who made it.)

The foil-faced yellow looking foam boards are (poured) expanded
polyisocyanurate. The facings applied to these boards are there to provide
structural strength during the manufacturing, handling & installation
processes. Otherwise they would tend to just break apart at random
locations. (It's natural yellow color is difficult to dye to any other
color.)

White styrofoam board is also available.

He also mentioned the foil faced air bubble plastic material. He said the
manufactuers of this product have not been able to prove that it has any
real 'R' value of any kind. The salesmen even suggested a good use would be
to stuff it in your shoes to keep your feet dry. He refuses to distribute
this product for these reasons.

Rusty O