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Weight of Poly Roof Insulation Board

Samantha Kemp

Roof insulation board helps to reduce your carbon footprint, keeps your home warm in the winter and cool in the summer and improves your home's energy efficiency. Poly roof board can refer to several types of foam board, including polystyrene, polyisocyanurate or Polyiso and polyurethane. Each type of roof insulation board offers its own set of advantages, and each has a slightly different weight. Factoring in the weight of your poly roof insulation board can help you decide which one is best for your roofing project.

General Information

Learn the different weights for poly roof insulation boards.

Foam insulation can be made through closed-cell or open-cell foam. Open-cell foam contains broken surfaces that air fills, making it softer and lighter. Open-cell foam insulation should not be used where it can absorb moisture. Closed-cell foam is much more stiff and dense. The cells are often filled with gas to increase the efficiency of the insulation, referred to as the R-value. This rating is a measurement of an insulation's resistance to heat flow. The higher the R-value, the less insulation and weight you will need to install.

Polyisocyanurate Foam Board

Polyisocyanurate foam board is often referred to under the name of Polyiso, a major brand that markets this form of insulation. Made from foam plastic, this insulation does not need a thermal barrier and is used for more than 70 percent of all roof insulation projects. Polyisocyanurate is a closed-cell foam and generally has a 2-pound-per-cubic-foot density. It has a general R-value of 5.56, but can go as high as 8. Due to its increased R-value, consumers can add a thinner layer of the insulation while still achieving a higher efficiency.

Polystyrene Foam Board

Polystyrene foam board is a closed-cell foam insulation that has a strong resistance to moisture absorption. Typically, foam densities for polystyrene foam board are 1.5 pounds per cubic foot. Although the R-value often depends on the material's density, the R-value for polystyrene foam board is usually about R-5 per inch.

Polyurethane Foam Board

Polyurethane is another closed-cell foam insulation board. This material has a high R-value around R-7 to R-8 per inch. As time goes by, however, air can replace the gas inside the insulation, resulting in a decreased R-value of 1 to 2. It typically weighs 2 to 3 pounds per square foot. It is sold in 12-pound, 15-pound, 20-pound and 30-pound densities.