Residential exterior wall insulation is the least expensive solution for reducing your heating and cooling bills. Because of rising energy costs, engineers and building planners are always looking for new methods of exterior insulation. There are several insulation products available that provide a higher R-value per inch for the exterior of your home.
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R-value is the thermal resistance of all materials. It is typically measured per inch of thickness for comparison reasons. A material's thermal resistance is a measure of how slowly it transfers heat and cold from one side to the other. A higher R-value per inch is desirable for exterior walls.
Aerogel is the highest R-value-per-inch insulation available to residential builders. It is made using silica by extracting the liquid through supercritical drying. The resulting insulation is a blanket that has extremely low thermal conductivity. Aerogel has an R-value of 10.3 per inch. This product is not commonly used because of its high cost.
Closed-cell polyurethane is a sprayed-in-place type of insulation. The material expands dramatically when sprayed, filling all air gaps. Polyurethane has the additional benefit of being both an air and a vapor barrier. Slowing the movement of air is the best way to insulate your home. This type of insulation is very combustible and must be covered with a fire barrier such as drywall. It has a R-value per inch of 6.0.
Polyisocyanurate is a closed-cell foam board that uses trapped refrigerant gases instead of air bubbles. These boards are often finished with foil on one or both sides. Polyisocyanurate boards are good in applications where space is limited but budget is not. They have a per-inch R-value of 7.0.