IIC is a cost competitive alternative to fiberglass insulation because sprayed foam insulation provides both insulation and air barrier.  Foam insulation eliminates steps for air-tightness detailing required in the application of fiberglass insulation (such as caulking, applying house wrap and vapor barrier, and taping joints). More and more new houses are constructed with spray foam insulation. To see if you should upgrade to spray foam use this heat loss calculator. Calculate the current R value of your house and then the R value of the foam you would like to test. Typically foam is a 50% or more savings in energy. Heat Loss Calculator