Consider this list of typical insulation materials and the average R-values per inch to get ... and the desired R-value. Work with an insulation contractor to determine the best type of insulation ...

The denser the foam, the more R-value per inch. On average, one inch of 2-lb. closed cell foam that has fully cured will perform at a R-6.8. That means a 2×6 wall cavity filled with five inches ...