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Everything homeowners, builders, and insulation contractors need to know about spray foam R-values — what they mean, how open-cell and closed-cell foam compare, which R-values meet code in every climate zone, and how ArmorThane’s ArmorFoam delivers up to R-7.0 per inch.
Closed-cell spray foam delivers R-6.0 to R-7.0 per inch — nearly double fiberglass — while creating a 100% air seal and adding up to 300% racking strength to wall assemblies. This guide covers every R-value number you need, IECC climate zone minimums, how-many-inches thickness charts, and ArmorFoam specs. Updated April 2026.
Written & Reviewed By
Manufacturer chemists and field engineers based in Springfield, MO. ArmorThane has formulated polyurethane coatings and spray foam systems since 1989, supporting certified applicators in 30+ countries.
What is the R-value of spray foam insulation? Closed-cell spray foam has an R-value of R-6.0 to R-7.0 per inch. Open-cell spray foam has an R-value of R-3.5 to R-3.8 per inch. Total R-value equals R-value per inch multiplied by installed thickness. ArmorFoam closed-cell achieves R-6.5 to R-7.0 per inch — among the highest of any commercially available spray foam system.
R-value is the measure of a material’s resistance to heat flow. The “R” stands for thermal resistance. The higher the R-value, the better the insulation performs at slowing heat transfer from warm areas to cold areas. In winter, a high R-value keeps heat inside your home. In summer, it keeps heat outside.
R-value is expressed as a number — R-3, R-13, R-38, and so on. These numbers are additive: two layers of R-13 fiberglass yield roughly R-26. With spray foam, the R-value is calculated per inch of thickness, and total R-value grows as foam is applied thicker.
The U.S. Department of Energy, the IECC, and every major building code in North America use R-value as the primary metric for insulation requirements. When a code says “walls must achieve R-15,” it cares about thermal resistance delivered at the completed installation — not which material you use.
R-value measures how well insulation resists heat flow. A higher R-value means better insulation. Spray foam closed-cell achieves R-6.0 to R-7.0 per inch — the highest of any insulation type on the market. This means you can achieve code-minimum requirements in thinner assemblies, preserving interior space and structural integrity.
R-value is measured under ASTM C518 (steady-state heat flux) or ASTM C177. The test measures heat flow through a material at a specific mean temperature (typically 75°F). The result is expressed in imperial units as (°F · ft² · hr / BTU) per inch, or as a total for the full tested thickness.
One critical detail installers and homeowners often miss: R-value is tested under laboratory conditions. In the field, moisture infiltration, air movement, and installation defects all reduce effective thermal performance. Spray foam’s air-sealing capability is why its real-world performance frequently exceeds what the published R-value alone suggests — it eliminates convective losses that undermine fiberglass and cellulose.
Nominal R-value is the published, tested value under ideal lab conditions. Effective R-value is what you actually get in the wall or roof assembly, accounting for air leakage, thermal bridging through framing, moisture, and installation quality. Because spray foam creates an airtight seal and adheres directly to framing and sheathing, its effective R-value is consistently closer to its nominal R-value than any other insulation type.
Spray polyurethane foam (SPF) comes in two primary types — open-cell and closed-cell — each delivering a fundamentally different R-value per inch. Understanding the difference is essential before specifying any spray foam system for a residential or commercial project.
Source: U.S. Department of Energy & International Energy Conservation Code (IECC)
Closed-cell spray foam achieves R-6.0 to R-7.0 per inch because of its sealed cellular structure. When the two-component polyurethane system reacts and expands, the gas cells that form are closed off and filled with a blowing agent (typically a low-GWP HFO) that has lower thermal conductivity than air. The result is a dense, rigid foam where heat cannot travel easily through either the cell walls or the gas inside.
Open-cell foam expands to about 100× its original volume. The cell walls rupture during expansion, creating an open, interconnected structure that is light, flexible, and excellent at air sealing — but its cells are filled with air, which conducts heat more readily. Hence the lower R-value of R-3.5 to R-3.8 per inch.
Because closed-cell foam delivers nearly double the R-value per inch compared to open-cell or fiberglass, you can hit the same total R-value target in half the thickness. This is critical in tight wall assemblies, roof decks with limited rafter depth, and crawl spaces where cavity depth is constrained.
The two types of spray polyurethane foam serve different purposes. Understanding which to specify — or when to use both — is one of the most important decisions in any insulation project.
Closed-cell spray foam is the right choice when you need the maximum R-value in the least amount of space, when you need moisture and vapor control, or when the assembly is exposed to the elements. Exterior wall cavities, unvented rooflines, crawl space encapsulation, basement rim joists, commercial metal building insulation, and any application that sees occasional wetting all benefit from closed-cell foam’s combination of high R-value, vapor retarder properties, and water resistance.
Open-cell spray foam excels in applications where cavity depth is generous, vapor-open assemblies are preferred, or sound dampening is the primary goal. Its extremely high expansion rate makes it ideal for filling deep cavities and attic floors quickly and economically. STC ratings of 45–52 in standard wall assemblies make it the preferred choice for media rooms, home theaters, and shared walls in multi-family construction.
Many high-performance building envelopes use both types together. A common assembly is 2 inches of closed-cell foam on the exterior face of the wall cavity (providing the vapor barrier and structural benefit) with open-cell foam filling the remaining cavity depth (providing additional R-value and sound dampening at lower cost). This delivers the strengths of each type where they are most needed.
The IECC divides the United States into eight climate zones, numbered 1 through 8. Zone 1 is the hottest (Miami, Hawaii) and Zone 8 is the coldest (interior Alaska). Every climate zone has published minimum R-value requirements for ceiling/attic, walls, floors, and basement/crawlspace assemblies.
FL, HI, TX Coast, AZ South
R-13 Walls · R-13 Floor
TX, GA, SC, AZ, CA South
R-20 Walls · R-19 Floor
MO, KY, NC, VA, CA North
IL, IN, OH, PA, WA, OR
R-20+5 Walls · R-30 Floor
MN, WI, MT, WY, ME, VT
ND, AK Interior
R-21+5 Walls · R-38 Floor
Many states adopt the IECC with amendments — some stricter, some less. California uses its own Title 24 code. Florida uses FBC-Energy. Always confirm your jurisdiction’s adopted code edition with your local building department before specifying insulation. ArmorThane technical support can help identify the right ArmorFoam system for your climate zone.
Using closed-cell ArmorFoam at R-6.5/inch as the baseline:
Beyond climate zone, the location within the building envelope determines the right target R-value and the right foam type. Different assemblies have different thermal dynamics, moisture exposures, and structural requirements.
The single biggest source of heat loss — up to 25% of total energy. Vented attic floors: R-38 to R-60. Unvented conditioned attics (foam on underside of roof deck): closed-cell at R-30+ provides both insulation and air barrier.
In a 2×6 cavity (5.5″), closed-cell at R-6.5/inch delivers R-35+. Open-cell in a 2×6 cavity provides R-20. Hybrid approach (2″ closed-cell + remaining open-cell) hits R-28+ with vapor control and cost efficiency.
Closed-cell provides R-value, vapor barrier, adheres to concrete without fasteners, and resists seasonal moisture cycling. 2–3 inches on rim joists is one of the highest-ROI insulation upgrades available.
Closed-cell foam on crawl space walls provides R-value, vapor control, and pest resistance. Code minimum is typically R-10 to R-15. Performance builders target R-15 to R-25 for crawl space walls using spray foam.
Closed-cell applied directly to metal panels eliminates thermal bridging at every purlin and girt, provides both insulation and air barrier, and eliminates condensation that corrodes the structure. R-19 to R-30 on roof panels is common.
Open-cell is preferred for interior walls between conditioned spaces due to superior sound dampening. For floors over unconditioned spaces, closed-cell on the underside provides R-value, vapor control, and structural benefit simultaneously.
Spray foam has a higher upfront cost than fiberglass or cellulose, but the total cost of ownership over the life of the building almost always favors spray foam. The key drivers: energy savings of 20% to 40% annually, a service life of 80 to 100 years versus 15 to 25 for fiberglass, and the elimination of separate air sealing labor and materials. When you add structural benefit and moisture damage prevention, the ROI calculation becomes compelling.
ArmorThane has been manufacturing polyurethane-based protective coatings and spray foam systems in Springfield, Missouri since 1989. ArmorFoam is ArmorThane’s own spray polyurethane foam formulation, engineered to deliver one of the highest R-values per inch of any commercially available spray foam while providing the airtight seal, structural reinforcement, and durability ArmorThane’s chemistry is known for.
As a manufacturer — not a franchise — ArmorThane controls every step from raw material chemistry to finished foam performance. ArmorFoam systems are installed by a global network of trained and certified ArmorThane dealers, supported by 24/7 technical support from the Springfield manufacturing facility.
ArmorFoam closed-cell delivers up to R-7.0 per inch — the highest thermal resistance available in a spray-applied insulation system. Code compliance in minimal thickness, preserving cavity space and structural integrity.
ArmorFoam expands to fill every gap, crack, and void in the building envelope. Unlike fiberglass batts that leave air pathways around framing, ArmorFoam eliminates convective heat loss — the primary reason insulation underperforms its rated R-value in the field.
Closed-cell ArmorFoam adds up to 300% racking strength to wall assemblies when fully adhered to both sheathing and framing — documented in third-party testing and can reduce or eliminate the need for additional structural sheathing.
Properly installed ArmorFoam does not settle, compress, or lose R-value over time. Unlike fiberglass which loses performance as it settles and air pathways develop, spray foam maintains its rated R-value for the life of the building.
Performance targets shown are typical ranges. Refer to the ArmorFoam Technical Data Sheet for project-specific specifications. Contact ArmorThane at (417) 831-5090 for TDS and SDS documentation.
Enter your target R-value and foam type to instantly calculate required inches of spray foam.
Code minimum is a floor, not a ceiling. Many building science experts recommend exceeding code minimums, particularly in climate zones 4 through 8. Here’s how to think about the right R-value target for different project types.
Your zip code determines your IECC climate zone. The DOE’s Energy Star Climate Zone Finder or your local building department can confirm which zone applies. Climate zones 1 and 2 (hot climates) have lower R-value requirements than zones 6, 7, and 8 (cold climates). Your baseline specification starts here.
Attic floor, roof deck, wall cavity, basement wall, rim joist, crawl space, and slab-on-grade all have different code requirements and different energy loss profiles. Attics typically require the highest total R-value (R-38 to R-49+) because heat rises and roof assemblies see the largest temperature differentials.
Closed-cell for exterior assemblies, moisture-exposed locations, and anywhere you need vapor control or structural benefit. Open-cell for interior partitions, deep attic floors, and sound dampening. Hybrid approaches for assemblies that need both vapor control and economical depth-filling.
Divide your target R-value by the R-value per inch of the foam selected. For closed-cell ArmorFoam at R-6.5/inch: R-21 target ÷ 6.5 = 3.2 inches. Round up to ensure you meet or exceed the target. Account for framing depth and any continuous insulation requirements in your jurisdiction’s code.
The marginal cost of an additional inch of spray foam during installation is small compared to cumulative energy savings over decades. Wall assemblies beyond code minimums — particularly in climate zones 5 through 8 — deliver measurable energy savings with payback periods of 5 to 8 years. Use our calculator above to model your specific project.
Spray foam insulation’s R-value performance is only as good as the installation. Unlike fiberglass batts that any homeowner can install, spray polyurethane foam requires professional application with specialized plural-component equipment. ArmorThane’s global dealer network brings certified, trained applicators to projects across North America and more than 30 countries.
ArmorFoam is a two-component system: an isocyanate A-side and a polyol blend B-side. When the two components meet at the spray gun tip in precise ratio, they react and expand into foam in seconds. Here is what a professional installation looks like:
Substrates must be clean, dry, and free of dust, oil, and incompatible materials. Concrete must be at or above 40°F. Wood framing should be at moisture content below 19%. All electrical penetrations should be roughed in and inspected before foam application.
Spray foam performs best when ambient temperature is between 60°F and 90°F and relative humidity is below 80%. Cold substrates can cause adhesion problems; hot, humid conditions can cause blistering and off-ratio reactions.
ArmorThane plural-component proportioners heat the A and B components to specified temperatures (typically 120°F to 140°F), pressurize to 1,000–2,000 psi, and deliver them in precise 1:1 ratio to the impingement-mixing spray gun. Equipment calibration is verified before every job.
The applicator applies foam in overlapping passes, building thickness in lifts. Closed-cell foam is typically limited to 2 inches per pass to manage exothermic heat. Open-cell foam can be applied in thicker lifts. The foam expands, self-levels at details, and adheres to the substrate within seconds.
Film thickness is verified by probe or depth gauge. Density is verified by cutting a sample cube and weighing it. Any areas below specification are recoated before the thermal barrier is installed. Building codes require a thermal barrier (typically ½” gypsum drywall) over spray foam in occupied spaces — ArmorThane applicators understand code requirements and ensure the installation is inspection-ready.
Unlike most spray foam brands that rely on third-party equipment, ArmorThane designs and manufactures its own plural-component proportioners, spray guns, heated hose assemblies, and mobile spray rigs in Springfield, Missouri. This means ArmorThane dealers get equipment optimized for ArmorFoam chemistry, with direct factory support for service and parts. Equipment and chemistry from the same manufacturer eliminates the compatibility issues that plague many spray foam installations.
Spray foam insulation comes in two types. Closed-cell spray foam delivers R-6.0 to R-7.0 per inch — the highest R-value of any commonly used insulation material. Open-cell spray foam delivers R-3.5 to R-3.8 per inch, comparable to fiberglass batts but with dramatically better air sealing. The total R-value is determined by multiplying the R-value per inch by the installed thickness. For example, 3 inches of closed-cell foam at R-6.5/inch delivers approximately R-19.5.
3 inches of closed-cell spray foam at R-6.5/inch delivers approximately R-19.5, which meets or exceeds wall code minimums in Climate Zones 1 through 4. 3 inches of open-cell foam at R-3.7/inch delivers approximately R-11, which is below wall minimums in most climate zones but provides excellent air sealing. ArmorFoam closed-cell at R-6.75/inch: 3 inches = R-20.25 — meets Zone 3-4 wall requirements exactly.
It depends on the application. In wall cavities where depth is limited (2×4 or 2×6 framing), closed-cell foam’s higher R-value per inch allows you to hit or exceed code in the available space. Open-cell foam in a 2×4 cavity (3.5 inches) delivers only R-13 — barely meeting Zone 3 minimums and falling short in colder zones. Closed-cell in the same cavity delivers R-22+. For attics with generous depth, open-cell is often more economical. For any moisture-exposed assembly, closed-cell is the correct technical choice regardless of cost.
IECC 2021 requires R-30 in Climate Zone 1-2, R-38 in Zone 3, and R-49 in Zones 4 through 8. For an unvented conditioned attic (spray foam on the underside of the roof deck), the minimum R-value is typically reduced — check your local code. Using closed-cell ArmorFoam at R-6.5/inch: R-38 requires approximately 5.9 inches; R-49 requires approximately 7.5 inches. Using open-cell ArmorFoam at R-3.7/inch: R-49 requires approximately 13 inches. Most performance builders targeting above-code performance specify R-49 to R-60 in climate zones 4 through 8.
Properly installed spray foam does not lose significant R-value over time under normal conditions. Closed-cell foam is dimensionally stable — it does not settle, compress, or degrade. Open-cell foam is slightly more susceptible to long-term R-value loss if it absorbs moisture, but in properly designed assemblies with appropriate vapor management, both types maintain their rated R-value for decades. This is a major advantage over fiberglass batts, which settle and lose effective R-value as they age and as air pathways develop around the framing.
Closed-cell spray foam delivers R-6.0 to R-7.0 per inch versus R-2.9 to R-3.8 per inch for fiberglass batts — approximately double the R-value per inch. But the more important comparison is effective R-value in the installed assembly. Fiberglass batts are notorious for air gaps, compression, and installation defects that reduce effective R-value by 20% to 50% compared to the nominal value. Spray foam, because it adheres directly to all surfaces and expands to fill every void, consistently delivers effective R-values close to its nominal rating. A spray foam assembly rated at R-20 typically outperforms a fiberglass assembly rated at R-30 in real-world energy use.
Two inches of closed-cell spray foam at R-6.5/inch delivers approximately R-13, which meets the wall cavity minimum in Climate Zones 1 and 2. It does not meet wall minimums in Zones 3 through 8 (which require R-20 or more). Two inches of closed-cell does meet the R-10 requirement for crawl space walls in most zones. For roof and attic applications, 2 inches is generally far below code minimums in any climate zone. Always verify the specific code requirement for your assembly type and climate zone before finalizing specifications.
R-21 is an excellent wall assembly R-value. It meets code minimums for Climate Zones 1 through 4 (which require R-13 to R-20) and comes within 5% of Zone 5-6 minimums (R-20+5 continuous). Using closed-cell ArmorFoam at R-6.75/inch, you achieve R-21 with approximately 3.1 inches of foam — fitting comfortably in a 2×4 or 2×6 wall cavity while leaving room for utilities. For zones 5-8, aim for R-21+ total with additional continuous insulation to meet the “+5” continuous requirement.
For most residential and commercial applications, yes. The higher upfront cost — typically $1.50 to $5.00 per square foot installed depending on type and thickness — is offset by 20% to 40% annual energy savings compared to fiberglass or cellulose. Most homeowners see full payback within 3 to 6 years. Beyond energy savings, spray foam provides air sealing, moisture management, structural reinforcement (closed-cell), and a service life of 80 to 100 years. When you factor in the cost of periodic replacement, air sealing labor, and separate vapor barrier materials that other systems require, spray foam’s total cost of ownership is frequently lower.
ArmorFoam closed-cell spray foam delivers R-6.5 to R-7.0 per inch, among the highest available for any commercially applied spray foam system. ArmorFoam open-cell delivers R-3.5 to R-3.8 per inch. Both values are determined by ASTM C518 testing and documented in the ArmorFoam Technical Data Sheet. For project-specific specifications, contact ArmorThane at (417) 831-5090 or request the current TDS through our website.
In most cases, yes. Spray foam can be applied over existing fiberglass, cellulose, or mineral wool insulation as long as the existing insulation is dry, clean, and securely in place. For open-cell foam applications on attic floors, spraying over existing blown-in cellulose is common. For wall retrofits, the existing insulation is typically removed before spray foam is applied to ensure proper adhesion and avoid trapping moisture. Contact ArmorThane technical support for project-specific guidance.
ArmorThane maintains a global network of trained and certified applicators across North America and more than 30 countries. To find a certified ArmorFoam installer in your area, call ArmorThane directly at (417) 831-5090 or submit a quote request through the ArmorThane website. ArmorThane will connect you with the nearest qualified dealer for your project type — residential insulation, commercial insulation, roofing, or industrial spray foam applications.
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ArmorFoam closed-cell systems — R-6.5 to R-7.0/inch with 300% racking strength and Class II vapor retarder.
ArmorFoam open-cell systems — R-3.5 to R-3.8/inch with STC 45-52 sound control and 100% air seal.
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