Have a question.  Not really sure what I have here, a friend gave me 34 sheets of Rigid foam insulation 1 3/4 thick yellow with a felt backing.  It has tiny holes in the felt on both sides not sure of the type has anyone seen this.  Was going to use it in the basement but not sure the install process.  thanks

sounds like polyisocyanurate. It's typically made with an aluminum foil facing for residential use, but is made with the asphalt felt for commercial roofing applications. What you have may be "used" and salvaged from a commercial roofing project - commonly available and still useable. Polyiso is good for gluing/ nailing to basement walls, but I'm unsure if the felt might absorb any moisture from the concrete and become moldy. Anyone have thoughts on that?

I agree it sounds like polyiso. Has a great r vaue per inch. I have used it in basements but that is in dry Colorado. If the framing/ furring isn't up it would be easy enough to put up 6 mil poly and then no problem.

Roofing poliso is the most likely suspect. At 1.75" figure it's about R10 at the temperatures seen in a basement in a heating dominated climate.

Fix it agianst the foundation with 1x furring through-screwed to the foundation with 3" TapCons 24" o.c., which gives you something on which to hang the gypsum. Don't let the edge rest on the slab or it'll wick ground moisture over time- but a half-inch of air is plenty of capillary break.