Hi,
I live in Maryland zone 4a Marine.

I am finishing my basement and using 1″ polyiso foam board as the thermal barrier for 2 reasons – it’s more fire retardant than the other foam boards and it has a higher R value/inch. (1″ polyiso=R6 v 1″ XPS=R5).  I read that polyiso loses R value in cold weather but that there isn’t a concern when used in interior applications.

I read that polyiso shouldn’t be used because it can wick up moisture.  However, I read that only happens if the polyiso is made with fiberglass.  I understand that RMax R Matte Plus 3 and John Manfield AP Foil Faced are two products that do not use fiberglass and therefore won’t absorb water.  I was going to raise the boards a half inch off the ground to be safe.

I also understand that since it is being used inside the basement, that it doesn’t matter which side is facing the interior v the concrete wall.

I would appreciate your thoughts/comments.
Thanks!
Sue