Can I use polyiso foam for interior basement wall insulation?
A recent GBA article (https://www.greenbuildingadvisor.com/community/forum/gba-pro-help/18454/what-best-way-insulate-interior-finished-basement-walls-have-2-ri) discussed options for internal foam insulation on a wall already with external insulation. Another article (https://www.greenbuildingadvisor.com/green-basics/rigid-foam-insulation) tells us that polyiso shouldn’t be used for below-grade applications because it can absorb water. Our design includes a poured basement wall with 4″ of internal XPS foam. I am concerned about external foam being mangled during backfill. I’d prefer to use polyiso over XPS because of the higher r-value per inch, but I’m not sure if it will work well for interior basement walls.