Insulation, Radiant and Vapor Barriers - Using Foam for Insulation

I have a BUNCH of upholestry foam and was wondering if anyone has ever used it for insulation or if anyone knows the pros or cons of doing so? What is the R value?

I am building a school bus into a motorhome and need to insulate the walls, floor and ceiling. Does anyone have a recommendation on what would be best? Of course, I am looking for the most economical way to do it but I also want it to be good insulation.

Thank you in advance for any and all input.

I've never heard of upholstery foam being used for insulating purposes before so it's hard to say how well it would work and I don't think there's any r value to it, as far as I know.
I suppose if it's the more expensive, high density kind, it would probably be better than the kind you buy at a fabric store, and I would think you'd have to put either some thick batting or Warm and Natural batting over it in order for it to be more effective. But by the time you buy the batting, it may be better just to use r board or insulation board available at HD or Lowes.
Maybe someone else knows for sure.