What is the R-value of Open Cell Foam?
Foam It Green open cell spray foam insulation is R-3.6 per inch. If using open cell to retro-fill a closed wall containing fiberglass batts, the open cell foam will condense to become a closed cell foam. In this application, the R-value is R-7 per inch cured.
Is this a vapor barrier?
Foam It Green is a Class III vapor retarder. Your local code will determine which Class vapor retarder you need. If your code requires a Class II or better, then hang kraft paper (comes in rolls at home stores) after you have sprayed the foam.