The short answer
Both insulate and air-seal, but they are not interchangeable. Open-cell foam is softer, more vapor-permeable and usually cheaper per board foot, at about R-3.6 to R-4.5 per inch. Closed-cell foam is denser, gives about R-5.8 to R-6.9 per inch and slows water vapor at specified thicknesses. Open-cell suits dry, deep above-grade cavities with a sound vapor strategy; closed-cell suits limited depth and assemblies that need vapor control. Roof decks depend on climate and drying.
For a typical dry, above-grade wall with plenty of cavity depth, open-cell foam can be a practical option. For a tight rim joist, below-grade wall or metal-building assembly where vapor control is important, closed-cell foam often has the advantage. Roof decks need more care: climate, roof coverings, existing insulation and drying potential can change the answer.
This guide compares the actual performance differences and shows what to ask an installer before signing a contract.
Quick verdict: Choose open-cell when cost and cavity-filling are the priority and the assembly is designed to manage vapor correctly. Choose closed-cell when available depth is limited, higher R-value per inch matters, or the assembly needs lower vapor permeance. Neither product fixes a leak or a badly designed building envelope.
Need the fundamentals first? Read the separate open-cell spray foam guide and closed-cell spray foam guide.
Open Cell vs Closed Cell Spray Foam: Comparison Table
| Feature | Open-cell spray foam | Closed-cell spray foam |
|---|---|---|
| Typical density | Roughly 0.5–0.8 lb/ft³ | Roughly 1.8–2.3 lb/ft³ |
| Typical R-value per inch | About R-3.6 to R-4.5 | About R-5.8 to R-6.9 |
| Cured texture | Soft and flexible | Rigid and dense |
| Expansion | Generally expands more | Generally expands less |
| Air sealing | Yes, at product-tested thickness | Yes, at product-tested thickness |
| Vapor behavior | Comparatively vapor-permeable | Lower permeance; may qualify as a vapor retarder at product-specific thickness |
| Bulk-water exposure | Not intended for wet conditions | More water-resistant, but not waterproofing |
| Depth needed for the same nominal R-value | More | Less |
| Acoustic performance | Can provide useful sound absorption | Not normally chosen for sound absorption |
| Typical relative material/installation cost | Lower | Higher |
| Common applications | Above-grade framed cavities and suitable roof assemblies | Rim joists, limited-depth cavities, certain below-grade and metal-building assemblies |
| Biggest design concern | Vapor control and moisture exposure | Restricted drying and trapping existing moisture |
Typical ranges from the Spray Polyurethane Foam Alliance (SPFA)[1]. Actual properties depend on the formulation, tested thickness and manufacturer documentation.
What Actually Makes the Two Foams Different?
Spray polyurethane foam starts as liquid components mixed at application. The material expands and cures into insulation adhered to the substrate.
In open-cell spray foam, much of the cell structure is open. The result is lightweight, flexible insulation whose cells contain air. In closed-cell spray foam, most cells remain closed and contain insulating gas, creating a denser product with higher thermal resistance per inch.
That cellular difference explains why the products behave differently. It does not mean one is inherently safe in every assembly and the other unsafe. Installed performance depends on the whole wall, roof or floor design, not just the foam.
Which Spray Foam Has the Better R-Value?
Closed-cell foam wins on R-value per inch. SPFA lists typical closed-cell products at roughly R-5.8 to R-6.9 per inch versus R-3.6 to R-4.5 for open-cell products[1].
That difference is commercially relevant when there is a shallow cavity. A two-inch space may not accommodate enough open-cell foam to meet the intended thermal target, while an appropriate closed-cell product may deliver significantly more insulation within the same depth.
R-Value by Thickness: Worked Examples
The table below uses illustrative midpoint values of R-3.7 per inch for open-cell and R-6.5 per inch for closed-cell. These are arithmetic examples, not guarantees for a specific product or proof of code compliance.
| Installed thickness | Open-cell at R-3.7/inch | Closed-cell at R-6.5/inch |
|---|---|---|
| 1 inch | R-3.7 | R-6.5 |
| 2 inches | R-7.4 | R-13.0 |
| 3 inches | R-11.1 | R-19.5 |
| 4 inches | R-14.8 | R-26.0 |
| 5.5 inches | R-20.4 | R-35.8 |
Example: To achieve a nominal material R-20 using those illustrative values, you’d need about 5.4 inches of open-cell or 3.1 inches of closed-cell foam.
But a whole-wall R-value is not simply the foam’s R-value. Studs and other framing conduct heat, and additional layers affect the final assembly. Local energy code may also prescribe continuous insulation, assembly performance or specific air/vapor requirements.
Ask for the exact manufacturer’s tested R-value at the quoted installation thickness, not a rounded marketing claim.
For a closer examination, see closed-cell spray foam insulation or open-cell spray foam insulation.
Open Cell vs Closed Cell Spray Foam Cost
Open-cell usually costs less per board foot: HomeAdvisor’s national installed ranges are $0.60–$1.60 for open-cell and $1.30–$3.10 for closed-cell[2]. But closed-cell reaches a given R-value with less thickness, so compare the cost of the same R-value, not the same inches, and include minimum charges, preparation and fire protection. The worked comparison is on the open-cell vs closed-cell cost page.
Which Foam Is Better for Moisture and Vapor Control?
Closed-cell foam generally has lower water-vapor permeance and greater resistance to bulk-water absorption.[1] That can be an advantage in particular basements, rim joists and metal-building assemblies.
Open-cell foam remains more vapor-permeable at common installation thicknesses. In a correctly designed assembly, that can support drying. In the wrong climate or location, it can also allow unwanted vapor movement toward a cold surface.
This is the part most simplistic product comparisons miss: more vapor resistance is not universally better. If a roof or wall already has low-permeance layers, applying more vapor-resistant insulation on the wrong side may reduce its ability to dry after a leak.
Is Closed-Cell Spray Foam Waterproof?
No. Closed-cell SPF is more water-resistant than open-cell foam, but it is not a substitute for drainage, flashing, waterproofing or fixing active leaks. It must not be sprayed over wet, rotten or contaminated material in the hope that the foam will solve the problem.
Does Open-Cell Spray Foam Need a Vapor Retarder?
Potentially. The answer depends on climate zone, product permeance, installed thickness and the wall or roof assembly. SPFA specifically notes that open-cell foam can require a separate vapor retarder in colder climates[1][3]. A contractor should explain the vapor-control strategy using the proposed product data and local code, rather than saying all open-cell foam “breathes” and therefore needs nothing else.
Can Spray Foam Hide Roof Leaks?
Yes, either foam type can complicate leak identification in some roof-deck arrangements. With closed-cell foam, reduced inward drying may be especially consequential in certain roof systems. Open-cell foam’s permeability does not make it a leak detector or a cure for an unventilated roof problem.
Before converting a vented attic into an unvented conditioned attic, have the full roof assembly evaluated. Read our attic spray foam insulation guide and roof-deck insulation guide.
Best Spray Foam by Application
The right foam for one part of a building may be the wrong foam just a few feet away.
| Application | Practical starting point | Why |
|---|---|---|
| Above-grade exterior framed walls | Either, assembly-dependent | Compare cavity depth, R target and vapor design |
| Interior partitions | Open-cell often considered | Cavity filling and sound absorption; acoustics still depend on the full wall |
| Rim joists | Closed-cell commonly considered | Compact area with air-leakage and condensation concerns |
| Basement foundation walls | Closed-cell often considered | Lower vapor permeance and greater water resistance |
| Crawl spaces | Closed-cell often considered | Moisture exposure and assembly detailing matter |
| Metal buildings | Closed-cell commonly considered | Condensation control, substrate and climate must be checked |
| Attic roof deck | Either may be possible | Roof-covering, climate and drying strategy govern |
| Shallow cavities | Closed-cell has an advantage | More R-value per inch |
| Dry, deep above-grade cavities | Open-cell may be economical | More space allows greater thickness |
These are selection tendencies, not universal specifications. SPFA documents residential applications for both types of foam and ties choices to assembly and code conditions. [3]
Attics and Roof Decks
An attic is not a single insulation scenario. Spraying the attic floor to keep the attic outside the conditioned envelope differs from spraying the underside of the roof to bring the attic inside it.
For an unvented roof assembly, open-cell foam may be appropriate in some climates and constructions, while closed-cell may be used where condensation and vapor control require it. DOE’s Building America guidance, for example, calls for a Class II vapor retarder over open-cell foam under the roof deck in climate zones 5 to 8[4]. Roof material, sheathing, exterior insulation, existing membranes, indoor humidity and the relevant code provisions are all part of the decision.
Don’t choose solely on “open-cell is cheaper” or “closed-cell has more R-value.” Ask the installer to document why the roof can dry safely with the proposed assembly.
Exterior Walls
Both products can seal irregular framing gaps when installed correctly. Open-cell may make financial sense where the cavity has enough depth to meet the planned performance. Closed-cell can be useful in tighter walls, but thermal bridging through framing still matters.
For new construction or a major renovation, compare the total wall assembly rather than the foam alone. Adding continuous exterior insulation, for example, can change which cavity insulation is most economical.
Basements, Crawl Spaces and Rim Joists
These locations put moisture management ahead of easy slogans. Closed-cell foam is often the stronger candidate because it combines air sealing with lower vapor permeance at tested thicknesses.
However, a crawl space with standing water, poor drainage or a basement wall that leaks needs a water-management fix first. Foam is not the first repair.
Learn more in crawl-space spray foam insulation, basement wall insulation and rim-joist spray foam.
Metal Buildings and Barndominiums
Condensation on metal can be a major design concern. Closed-cell foam is frequently specified for its adhesion and lower vapor permeance, but the right thickness and location depend on the metal building’s structure, climate and intended indoor conditions.
A conditioned barndominium with living space has different requirements from an unconditioned workshop. Compare the entire envelope and its ventilation strategy rather than automatically using one foam everywhere.
See barndominium spray foam insulation for the application-specific decision.
Is Open-Cell Spray Foam Better for Soundproofing?
Open-cell foam can absorb sound inside a wall cavity, but it is not a complete soundproofing system. The outcome depends heavily on wall mass, decoupling, sealing and penetrations.
For an interior partition, open-cell foam may be attractive where thermal resistance is secondary and acoustic absorption matters. However, mineral wool or other cavity insulation paired with appropriate drywall and wall construction can also perform well.
Avoid promises such as “open-cell eliminates outside noise.” Ask for the acoustic performance of the complete tested assembly, not just the foam.
Is Closed-Cell Spray Foam Stronger?
Closed-cell foam cures into a rigid material, and manufacturers describe it as adding stiffness to some framed assemblies. That does not make it a substitute for engineered structural bracing, unless an engineer has assessed a tested system and applicable approvals.
Open-cell foam remains more flexible and should not be marketed as structural reinforcement.
Installation and Safety: What Both Foams Have in Common
Both are two-component spray foams, and installation quality matters as much as the product. Occupants should be out during spraying and should return only on the specific product’s re-occupancy instructions, not a blanket 24-hour promise. Both need the thermal or ignition protection the code requires for that location. See is spray foam insulation safe? and spray foam building codes.
How to Choose Between Open-Cell and Closed-Cell Foam
Work through this decision sequence rather than accepting the contractor’s favorite product by default.
1. Identify the assembly. Is this a wall cavity, roof deck, rim joist, basement, crawl space or metal building? The same product can be appropriate in one assembly and unsuitable in another.
2. Establish the required performance. Get the code-required thermal target and any required air-barrier or vapor-control specifications.
3. Check the available cavity depth. If the full insulation target must fit into a thin space, closed-cell’s greater R-value per inch becomes more valuable.
4. Map the moisture and drying paths. Identify exterior membranes, roof coverings, damp substrates, indoor humidity and whether the assembly must dry inward or outward.
5. Obtain like-for-like quotes. Request thickness, exact product, tested R-value, fire-protection requirements and full installed price.
6. Check the installation plan. Confirm training, ventilation, occupant exclusion, documented re-occupancy instructions, warranties and post-install inspection.
7. Choose the assembly, not the sales pitch. A documented, code-compliant proposal with an explainable moisture strategy beats “we always use closed-cell” or “open-cell is good enough everywhere.”
Questions to Ask a Spray Foam Contractor
Ask each bidder:
- What exact foam manufacturer and product are you proposing?
- What is its published R-value at the thickness you will install?
- Will this assembly meet local energy and building-code requirements?
- Is this an air barrier at the proposed thickness?
- What is its published vapor permeance at the proposed thickness?
- Where can any incidental moisture dry?
- How will you inspect for leaks or damp sheathing before spraying?
- Do we need a thermal barrier, ignition barrier or protective coating?
- What are the ventilation and re-occupancy requirements for this particular product?
- What are the full installed cost, minimum thickness tolerance and workmanship warranty?
Our guide to choosing a spray foam contractor expands on quote comparison and quality checks.
Open Cell vs Closed Cell: Final Verdict
For a dry, deep cavity with a sound vapor-control design, open-cell foam is often the more economical way to achieve air sealing and insulation. For a shallow cavity, high moisture-exposure location or assembly requiring lower vapor permeance, closed-cell foam often earns its premium.
For attic roof decks and complex retrofit walls, there isn’t a reliable universal winner. Roof construction, local climate, existing membranes and drying potential are what decide it.
If you’re comparing quotes, ask for the exact assembly specification, not simply a price per square foot. Then use the spray foam cost calculator to estimate quantities and prepare your questions before requesting a contractor proposal.
Ready to compare installation quotes? Start with our spray foam contractor directory and request itemized proposals using the same performance requirements. Spray Foam Guide does not install insulation.
Questions owners ask
Is closed-cell spray foam better than open-cell?
Not for every project. Closed-cell has more R-value per inch, higher density and lower vapor permeance. Open-cell is typically less expensive and can suit dry above-grade cavities where sufficient depth and a suitable vapor-control strategy are available. The correct choice is assembly-specific.
Which is cheaper, open-cell or closed-cell spray foam?
Open-cell is usually less expensive per board foot. However, closed-cell achieves a higher R-value in less thickness. Compare total installed cost for an equivalent design, not prices for unequal insulation thicknesses.
What is the R-value of open-cell versus closed-cell foam?
SPFA lists typical open-cell spray foam at about R-3.6 to R-4.5 per inch and closed-cell at approximately R-5.8 to R-6.9 per inch. Manufacturer test data and the quoted thickness determine the actual project value.
Can open-cell spray foam be used in an attic?
Yes, in appropriately designed attic and roof assemblies. Climate, the location of the insulation, roof-deck drying and vapor-retarder requirements determine suitability. Do not assume that any open-cell roof-deck application will be code-compliant.
Is closed-cell foam a vapor barrier?
Closed-cell foam can qualify as a vapor retarder at specified thicknesses, but do not assume every product is an absolute vapor barrier. Check the manufacturer's permeance data and the applicable code classification.
Which foam should I use in a crawl space?
Closed-cell is often evaluated first because crawl spaces can have significant moisture exposure. However, drainage, ground vapor control, humidity and the full crawl-space design must be addressed before spraying.
Can you mix open-cell and closed-cell spray foam?
Some designed assemblies may use different insulation materials in layers or different locations, but compatibility, drying potential and condensation control must be checked. Do not improvise a hybrid assembly without product and building-science guidance.
Sources
- Frequently Asked Questions, Spray Polyurethane Foam Alliance (SPFA). Accessed October 19, 2026. Industry trade association. Page metadata shows modified April 27, 2026. Typical density, R-value per inch, air-barrier thickness and vapor permeance ranges.
- How Much Does Spray Foam Insulation Cost?, HomeAdvisor. Accessed October 19, 2026. National consumer cost guide, updated June 17, 2026. Installed cost per board foot; national ranges, not quotes.
- Residential Applications, Spray Polyurethane Foam Alliance (SPFA). Accessed October 19, 2026. Industry trade association. Modified September 24, 2026. Application table references the 2018 IRC/IECC.
- Unvented Conditioned Attic with Spray Foam Insulation Below Roof Deck, U.S. Department of Energy, Building America Solution Center. Accessed October 19, 2026. DOE guide for new homes. No date shown.