Wake up senile nick, R value is R value, a standardised measurement used
to measure insulations effectiveness, resistance to heat flow. Polyiso
foilfaced, Both Sides is R 7.2" new, 6.8R" stabilised. Your mythical
dreamworld of R 6 added with 2 sheets of foil does not exist anywhere in
reality or at any store on this planet, or it would be sold as R 12.8*
polyiso, and it is not.