The millions of microscopic bubbles mentioned previously are filled with a gas in closed cell foam. This results in foam that is much denser than open cell foam and offers a much higher R-value at 6.5 per inch. Significant advantages of closed cell foam are its structural strength and its ability to deal with moisture effectively. The high R-value per inch allows you to install up to R-32 in an exterior 2×6 wall or R20 in a 2×4 wall. Closed cell foam is the only insulation that should be placed in moisture prone areas such as below grade concrete or on surfaces where tight adhesion are of significant importance such as steel buildings. Closed cell insulation generates no waste, is made from renewable and recycled materials and significantly reduces your carbon footprint making it possibly the greenest insulation available on the market. Make no mistake; closed cell spray foam insulation is the absolute best insulation in the world!!!!!