Rigid Foam Insulation for Interior Application


Is it plausible to insulate between the studs with fiberglass and then use rigid sheets of polyiso on the face of the studs to act as a thermal barrier as well as an insulator?

I’m thinking of using un-faced high density fiberglass (r15)along with 1/2" polyiso (r3.5)which will be covered by 1/2" Sheetrock® as a finish wall covering...


Hi Jack,

So that folks will know, “Polyiso is a closed-cell, rigid foam board insulation consisting of a foam core sandwiched between two facers. It is one of the three main types of foam insulation. (Read article & watch the videos at “Rigid Foam Insulation”).
Installing insulated foam sheathing on the interior walls of a pre-existing basement helps prevent heat loss and moisture problems, but I have never heard of using rigid foam insulation on the inside of an (exterior) stud wall.

My first concern was how you would hang drywall (Sheetrock®, gypsum board) over the rigid foam.

So, I asked my friend and architect David Moore of Original Home Plans what he thought.
Here is his reply:


Rigid foam is often applied in our area on the exterior of the wall where it acts as a thermal break to keep framing members from conducting heat or cold to the interior.

I have also applied rigid foam to the interior of the framing, as Jack describes. You do have to be careful when attaching gypsum board over the foam not to overdrive the fasteners and create a pillowed surface.


Well Jack, we both learned something today…I think.