What is the R-Value of 3 Inch Spray Foam Insulation?


Spray foam insulation offers more effective heat management by creating an air seal to block heat transfer from entering and leaving your home, which makes it more cost-efficient than its alternatives. What do you need to consider about spray foam r value.

Foam board insulation such as XPS or EPS boasts an outstanding R-value per inch due to its dense composition.


The R-value of foam board insulation measures its ability to keep conditioned air inside (warm air during summer and cool air during winter). The higher its R-value is, the more heat retention capabilities it possesses; however, R-value should not be the sole criterion you consider when choosing the appropriate foam board insulation product for your home; you must also factor in air sealing properties, moisture & mildew resistance, thermal drift capabilities, and other considerations as well.

Rigid ISO foam boards can provide highly high R-values. Styrofoam (XPS), the famous trademark name of tough ISO foam insulation material, comes in various thicknesses with R-values ranging from 5.2 per inch depending on thickness to 6 per inch for polyisocyanurate insulation – often used for house sheathing on walls and roofs due to its strength, durability, and adhesive-like adhesion properties.

Spray foam insulation offers a higher R-value than rigid insulation because it is impervious to moisture and won’t degrade over time. However, one inch won’t provide an air seal; contractors install two or more inches for optimal R-value in walls or roofs.

In many instances, roofs will contain saturated areas that must be addressed before spray foam installation. If this happens, contractors typically add an R-value increase of 6.5 for every inch of spray foam used on a roof.


Foam board insulation comes in various thicknesses. While thickness affects the R-value, other factors also affect performance. Rigid foam typically boasts a higher R-value per inch than other insulation forms, such as closed-cell spray foam with R-values up to 8.0, much higher than cellulose or fiberglass insulation. Foam board insulation strengthens walls or ceilings while resisting moisture retention and retarding vapor emissions.

The R-value of foam depends on its density and firmness; this value also changes depending on its application; for instance, guest room chairs might require lower densities than sofas in family rooms. Foam with higher densities tends to be heavier and costlier yet will last longer.

When purchasing foam for your home, please pay attention to its R-value per inch and thickness. The higher its R-value is, the more effective its insulation will be. Foam board insulation with high R-values features denser, thicker materials than traditional insulation materials – offering energy savings of up to 50 percent over conventional materials! Foam board also maintains its R-value over time more reliably than other types – which may lose as much as 8 percent due to heat absorption/radiation over time.


Installing three inches of spray foam over existing insulation with an R-value of 10 per inch will result in an R-value increase of 19.5 (6.5 x 3). While this upgrade offers significant energy savings, it should be remembered that R-value alone does not ensure sufficient insulation; suitable materials provide more than simply R-value insulation by sealing air leaks and resisting moisture build-up and vapor retarding properties.

Closed-cell spray foam insulation typically installed into walls offers an R-value of 6.5 per inch and superior performance to less-efficient insulation types like cellulose and fiberglass. Unfortunately, however, closed-cell spray foam is both flammable and off-gasses formaldehyde – both are considered harmful by some homeowners; additionally, some brands of closed-cell spray foam may have lower R-value after initial tests performed by manufacturers, which could pose issues for those suffering from allergies, or asthma.

Foam board insulation from ISO has an R-value of 7.0.1 per inch, while IKO’s EnerfoilTM foil-faced polyisocyanurate insulation boasts an even greater R-value of 8.0.0 per inch.

Flexible foam boards also boast relatively stable R-values over time, such as GPS insulation made of expanded polystyrene foam infused with graphite particles – its initial R-value per inch was initially set at 4.7. There was minimal thermal drift over 20 years compared with fiberglass insulation which can lose up to 8% of its initial value over this timeframe.


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Foam board insulation boasts many advantages over fiberglass batt insulation, such as its higher R-value per inch of thickness and resistance to moisture. Furthermore, its wide variety of shapes and sizes makes it suitable for homes or commercial structures – polyurethane foam insulation can fill rim joist spaces above foundation walls. In contrast, rigid polystyrene (EPS) type foam can block holes through exterior wall studs and more!

Foamed cellulose insulation can also help insulate unfinished attics and basements. However, its R-value ranges between 3.1 to 4.3 per inch of thickness compared with 4.3 for foam insulation, effectively stopping heat transfer through convection and air movement processes.

Spray foam insulation offers a high R-value per inch of thickness – up to R-6.5 per inch in some instances – yet its effectiveness depends on how it is installed and exposed to different environments. Over time, its R-value may diminish due to chemical blowing agents that break down over time, so for optimal results, installers must adhere to manufacturer specifications when installing and applying their foams correctly.

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