Blown in insulation, fiberglass and sprayed foam insulation are the most effective forms of attic insulation. Sprayed foam insulation offers the highest insulation value of the three types.
Blown in insulation is normally made from shredded paper and offers an insulation value that averages R-3.2 per inch of insulation. Fiberglass insulation offers R-2.9-R4.3 per inch depending on the density of the batts installed. Spray in foam can yield an R-value of 6 per inch. Sometimes attics are insulated using several different types of insulation. For example, foam insulation may be used between roof rafters and blown in insulation may be used on the attic floor.