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Protecting Your World

Understanding Spray Foam: Open Vs. Closed, Density & R-Values



You’re at the right place if you aim to learn about spray polyurethane foam insulation. Before using a spray foam application on a project, it is important to establish whether you will use .05 lb./cu. ft., open-cell spray foam or 2.0 lb./cu. ft. closed-cell spray foam. The differences are significant when factoring in performance, method of application, and price.

There are two principal factors to weigh when deciding between open-cell or closed-cell foam. First off, it is essential to study each type of foam. With open-cell foam, the tiny cells of the foam are not entirely closed, so the foam itself is porous and can fill with air and moisture. These tiny open spaces render the foam weaker and softer than closed-cell foam. Unlike open-cell spray foam, closed-cell foam has all the tiny cells of the foam sealed. The cells possess a gas that provides the spray foam with the capability to expand and better insulate a structure. During the formulation process, the cells are developed to have certain characteristics.

Open-cell spray polyurethane foam, sometimes called half-pound foam, has a typical density of 0.5 lb. per cubic foot and a typical R-value of 3.5 or 3.6 per inch.

Closed-cell foam, also called two-pound foam, has a typical density of 2 lbs. per cft and an R-value of 6-6.5 per inch.

Open-cell spray foam has an average density of 0.5 lbs per cubic foot. It delivers a typical R-Value of 3.5 to 3.6 per inch. Since the open cells are somewhat vapor-permeable, three inches of open-cell foam have a permeance of 16 perms. It often requires a vapor retarder when utilized in internal applications.

Closed-cell foam is itself a vapor retarder. It is vapor semi-impermeable. Two and a half inches of closed-cell foam have a permeance of 0.8 perms.

Open-Cell spray foam utilizes water or C02 as a blowing agent. Some open-cell foams, especially those with low density, use bio-based raw materials, such as sucrose or soybean oil rather than petrochemicals. Closed-cell Spray foam uses blowing agents that are hydrofluorocarbons (HFCs) with a high global warming potential. Because the global warming potential of these damaging blowing agents is 1,430 times more powerful than carbon dioxide, many manufacturers are swapping to more environmentally friendly Hydrofluoroolefins (HFOs).

There are three distinguishable levels of density one can choose from when it comes to spray foam insulation—high-density spray foam insulation, medium-density spray foam insulation, and low-density spray foam insulation. Each separate spray foam density is designed for a particular job and offers unique benefits. As such, it is important to educate yourself with the various densities so that you can choose the correct spray foam insulation type for your project.



High-density spray foam insulation has the densest structure of all spray foam insulation types. Due to its high density, more material is required to cover and insulate an area. For each cubic foot of high-density spray foam insulation, roughly 3 lbs. of closed-cell foam is used. In comparison to lower-density foams, high-density spray foam insulation doesn’t expand as much because of its denser structure. The R-value of high-density spray foam starts at around 5.5 per inch.


High-density spray foam insulation is utilized when an extremely high R-value and extra strength is required. Typically, high-density spray foam insulation is frequently employed for exterior and roofing applications in commercial or industrial construction.


High-density spray foam is applied in a steady manner, which results in a seamless application. Because of its impeccable thermal resistance properties, high-density spray foam insulation can immensely help reduce energy costs inside a structure throughout the lifetime of the roof it is applied to.

In addition to its exceptional insulating qualities, high-density spray foam insulation can also help safeguard and extend the life of roofing and exterior structures. Once bonded to a surface, high-density spray foam insulation can help lessen wind damage by increasing the structure’s resistance to wind uplift. Plus, it also helps shield the roofing against heat and water infiltration while simultaneously strengthening and providing load support to the structure it is applied to.




Medium-density spray foam insulation requires around 2 lbs. of closed-cell spray foam per cubic foot. It has a high R-value, which starts at 5.7 per inch.

Depending on the application, medium-density spray foam insulation can be used as either low- or high-pressure two-component spray foam insulation. For more expansive projects such as renovations or building construction, medium-density spray foam will likely be sprayed as high-pressure, two-component spray foam. For insulating small to midsized sites such as around ductwork or piping, medium-density spray foam is typically applied as low-pressure, two-component spray foam.


Medium-density spray foam insulation is oftentimes used for continuous insulation, unvented attic applications, and interior wall cavity fill. It is also the most common type of spray foam insulation utilized in crawlspaces and in the construction of new homes. Due to its high R-value of 5.7 per inch, medium-density spray foam insulation is frequently used in situations where the maximum possible R-value insulation per inch is needed.


Medium-density spray foam insulation delivers high-tensile strength, which means it will be able to withstand large amounts of stress without breaking—a beneficial quality for applications that require a durable insulation option. In addition, medium-density spray foam insulation also delivers a high bond strength. In other words, medium-density spray foam insulation adheres well to the surface it is applied to and requires a substantial amount of stress to separate the insulation from its base.

Further, medium-density spray foam insulation provides low vapor penetration. As such, its insulation markers aren’t typically degraded when exposed to moist environments or rain.

As previously stated, medium-density spray foam insulation also has an exceptionally high R-value. The R-value of an insulator calculates how well it is able to resist the conductive flow of heat—aka how effective it is as an insulator. At an impressive R-value of 5.7 per square inch, medium-density spray foam insulation is optimal for tight applications that require the highest possible R-value in the least amount of space.



An effective insulator, it provides continuous insulation and an air-sealing barrier to the surface it is applied to. As such, it can virtually seal airflow through joints, seams, cracks, and cavities. While low-density spray foam insulation acts as an air barrier, it is permeable to moisture and vapor because of its open-cell structure. By permitting for moisture permeability, low-density spray foam insulation helps streamline moisture control as well as bi-directional drying when necessary.

The large open-cell structure of low-density spray foam insulation allows it to stay relatively soft and provides some flexibility to the cured foam. This flexibility can be beneficial as it allows the insulation to retain its efficiency even as the structure it is applied to shifts and settles over time. As a perk, the soft texture of low-density spray foam insulation also helps absorb sound in the area it is applied to.

If you’re interested in installing spray foam insulation in your home or commercial building, make certain to enlist the help of a trained insulation installation professional. Spray foam insulation installation implicates complex processes that require specialized equipment and expertise. At ArmorThane, our trained contractors have the experience necessary to help you determine the appropriate spray foam insulation density for your application and install it safely and efficiently. For more information regarding our spray foam insulation contractors, contact us today.

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