Open-cell vs closed-cell spray foam: cost, R-value and where each one belongs (October 2026)

Prices and code sources checked October 20, 2026.

Open-cell spray foam costs $0.60 to $1.60 per board foot installed, and closed-cell spray foam costs $1.30 to $3.10, according to Angi's 2026 figures. Closed-cell foam packs roughly twice the R-value into each inch (R-6.8 to R-7.1, against R-3.6 for open-cell), so once you price both to the same R-value they land within a few cents of each other: $0.17 to $0.44 per R per square foot for open-cell and $0.18 to $0.46 for closed-cell. The bigger difference is water. Open-cell foam lets vapor pass and can soak up liquid water. Closed-cell foam slows vapor to under 1 perm at about 2 inches and does not absorb water.

We found no published source that prices open-cell and closed-cell foam on the same job, so we priced one ourselves. Every dollar figure on this page below the side-by-side table is our own math on a sample house, with the formula shown.

Open-cell vs closed-cell spray foam, side by side

Sources: Angi, "How Much Does Spray Foam Insulation Cost? [2026 Data]" (updated Sep 9, 2026); HomeGuide, "How Much Does Spray Foam Insulation Cost? (2026)" (Dec 1, 2025); Profoam product price sheet (R-value per inch column); U.S. DOE Building America, "Which Spray Foam Is Right For You?" (CARB / Steven Winter Associates, 2009); DOE/PNNL Building America Solution Center, Below Deck Spray Foam Insulation for Existing Roofs; FEMA, NFIP Technical Bulletin 2, Flood Damage-Resistant Materials Requirements (January 2025); eCFR, 40 CFR 84.54, Restrictions on the use of hydrofluorocarbons.

The cost-per-R row is the one most comparisons skip. Per board foot, closed-cell foam costs about twice as much. Per unit of R-value, Angi's ranges put the two foams almost level, because closed-cell needs about half the depth. A quote gap between the two usually comes from the depth each bidder chose, so check the inches before you compare totals.

What each foam costs on the same house

Our sample house is made up for illustration. It is not an average home:

• Attic floor: 1,600 sq ft.
• Roof deck: a 6/12 slope over that footprint, 1,600 × 1.118 = 1,789 sq ft, not counting the gable ends.
• Crawl space: a 40 by 40 foot footprint, so 160 feet of perimeter. Walls are 3 feet tall plus about 9 inches of rim joist, so 160 × 3.75 = 600 sq ft of foam surface.
• Rim joist only (for a house with a basement): 160 × 0.75 = 120 sq ft.
• Exterior walls: 1,200 sq ft net of windows and doors, with the cavities open.

The math: inches needed = R target ÷ R per inch. Board feet = area × inches. Cost = board feet × Angi's low or high rate, rounded to the nearest $100. For closed-cell, the thinner depth (R-7.1 per inch) pairs with the low rate and the thicker depth (R-6.8) with the high rate.

Four notes on that table:

• At the same R target, closed-cell foam costs $0 to $1,500 more than open-cell on these jobs. The widest gap is the R-49 roof deck: $1,500 at the low end and $1,000 at the high end.
• A full-depth open-cell roof deck at R-49 may not be buildable. DOE's guide says open-cell is generally sprayed up to 10 inches in one pass and that allowed roof thickness runs 5.5 to 10 inches, depending on each product's evaluation report. At 13.6 inches, ask the bidder which report allows that depth.
• The rim joist job is too small to price this way. HomeGuide says most spray foam companies charge a minimum of $1,000 to $2,000 or more, and lists rim joists at $2,000 to $2,500. Expect the minimum, not $300.
• Open-cell foam in a crawl space is priced only for comparison. See the crawl space section for why most guidance points to closed-cell there.

HomeGuide's per-square-foot prices don't state a depth. If its open-cell price covered a filled 2x4 cavity (3.5 inches), it would work out to $0.43 to $1.00 per board foot. If its closed-cell price covered 2 inches, it would be $1.50 to $2.50 per board foot. Both sit inside or near Angi's ranges.

Sources: Angi, "How Much Does Spray Foam Insulation Cost? [2026 Data]" (updated Sep 9, 2026); HomeGuide, "How Much Does Spray Foam Insulation Cost? (2026)" (Dec 1, 2025); U.S. DOE Building America, "Which Spray Foam Is Right For You?" (CARB / Steven Winter Associates, 2009).

Moisture is the real difference

The IRC sorts vapor retarders into three classes, as DOE/PNNL quotes it: Class I at 0.1 perm or less, Class II from 0.1 to 1.0 perm, and Class III from 1 to 10 perms. DOE's Building America guide puts open-cell foam at 5 to 10 perms at 5 inches, so open-cell is not a vapor retarder by the 1-perm definition the guide uses. Closed-cell foam tests under 1 perm at 2 inches, which DOE's guide treats as a vapor retarder.

Liquid water splits them further. Open-cell foam can hold water up to about one-third of its volume, from vapor diffusion, air leaks or roof and plumbing leaks, and it dries out again given time. Closed-cell foam sheds water. That cuts both ways on a roof: DOE's guide warns that a leak under closed-cell foam may not show up right away, which makes a worn roof harder to diagnose.

Humid metros feel this most. NOAA's Comparative Climatic Data average 89% relative humidity in the morning at Houston Intercontinental, 86% at Tampa International and 84% in Nashville, against 46% in Phoenix. In mapped flood zones, FEMA's Technical Bulletin 2 lists "closed-cell plastic foams" as acceptable below the base flood elevation and "open-cell plastic foams" as unacceptable. The same acceptable row also names sprayed polyurethane foam without saying which type, so ask your local floodplain office before any foam goes below that line. Our Houston cost page covers the flood rules there, and the Tampa and Nashville cost pages price local attics and crawl spaces.

Sources: DOE/PNNL Building America Solution Center, Below Deck Spray Foam Insulation for Existing Roofs; U.S. DOE Building America, "Which Spray Foam Is Right For You?" (CARB / Steven Winter Associates, 2009); NOAA NCEI, Comparative Climatic Data, average relative humidity (data through 2023); FEMA, NFIP Technical Bulletin 2, Flood Damage-Resistant Materials Requirements (January 2025).

Where each foam wins, part by part

DOE's Building America guide, written by the Consortium for Advanced Residential Buildings (Steven Winter Associates), rates each foam for each part of a house. Below are its ratings, with local facts from our cost pages.

Attic roof deck (sealed attic)

DOE rates closed-cell foam "preferred" under the roof deck in all climates and open-cell "acceptable" in cold and hot-humid climates. Closed-cell reaches high R-values within the thickness limits and adds wind resistance to the roof deck. Open-cell is cheaper per board foot and lets a roof leak dry toward the inside.

Local code can change the depth more than the foam does. In Georgia, foam under the roof deck can stop at R-20 when the house meets four state conditions, against R-38 on a vented attic floor, which our Atlanta cost page prices. Many Phoenix homeowners are quoted foam under the roof deck rather than on the attic floor (Phoenix cost page). In Tucson, TEP's 2026 rebate is built around R-38 and R-49, so a thin roofline job leaves that rebate unclaimed (Tucson cost page).

Attic floor (vented attic)

Full-depth foam on an attic floor is not common, per DOE. Open-cell foam's R-value per inch is "not much higher than far less expensive choices such as cellulose and fiberglass," and DOE prefers a thin closed-cell air-sealing layer here. It adds that 1½ inches of blown fiberglass over the foam counts as an ignition barrier under the IRC. In Colorado Springs, CSU's rebate needs R-49 in the attic, which is 13.6 inches of open-cell or 6.9 to 7.2 inches of closed-cell (Colorado Springs cost page).

Exterior walls

DOE rates both foams "preferred" in cold-climate and hot-dry walls. In hot-humid walls it rates closed-cell "preferred" and open-cell "acceptable", because open-cell needs careful moisture control there. A 2x4 wall is where open-cell falls short on R-value: filling 3.5 inches gives R-12.6. Colorado Springs Utilities pays its wall rebate at R-13 for the wall cavity, so a filled open-cell 2x4 wall misses it. A filled 2x6 wall reaches R-19.8 with open-cell foam.

Crawl space walls and rim joists

For foundations and below-grade spaces, DOE rates open-cell foam "not acceptable" and closed-cell "preferred". At band joists it rates closed-cell "preferred" and open-cell "acceptable", with closed-cell preferred in hot-humid or extreme cold climates. Angi also lists closed-cell as the best fit for crawl spaces and basements. CSU's crawl space rebate asks for R-15 continuous insulation plus a Class I vapor retarder; closed-cell reaches R-15 at 2.1 to 2.2 inches.

Basement walls

DOE again rates open-cell "not acceptable" and closed-cell "preferred" against the foundation, because water-tolerant insulation pressed to the wall keeps moist room air off the cold concrete. In a basement, DOE says the closed-cell foam must be covered by a thermal barrier. It describes a finished-basement option of 2 inches of closed-cell against the foundation, then framing, batts and drywall.

Flood-prone areas

Below the base flood elevation in a Special Flood Hazard Area, FEMA's bulletin lists closed-cell plastic foams as acceptable and open-cell plastic foams as unacceptable. Above the flood line, that FEMA list doesn't apply.

Sources: U.S. DOE Building America, "Which Spray Foam Is Right For You?" (CARB / Steven Winter Associates, 2009); Angi, "How Much Does Spray Foam Insulation Cost? [2026 Data]" (updated Sep 9, 2026); Colorado Springs Utilities, Residential rebate program rules; FEMA, NFIP Technical Bulletin 2, Flood Damage-Resistant Materials Requirements (January 2025).

Fine print before you sign

We could not read the ICC's own code site, so the IRC points below come from DOE/PNNL's Building America pages and an ICC Q&A sheet, which quote the 2009 to 2018 editions. Your city may enforce a different edition or local amendments; your building department has the final word.

1. Fire protection (IRC R316). Both foams are combustible. DOE's guide says the IRC calls for a 15-minute thermal barrier, the equivalent of ½-inch gypsum board, in most uses. In an attic entered only for repairs or maintenance, the 2009 IRC (R316.5.3) accepts an ignition barrier instead, such as 1½ inches of mineral fiber insulation, ¼-inch wood structural panel or ⅜-inch gypsum board. Some foams are tested to skip the ignition barrier (R316.6), and that is product by product. If you plan to store things in the attic, tell the bidder.
2. Cold-climate walls (IRC R702.7). In the IRC text DOE/PNNL quotes, frame walls in climate zones 5 through 8 and Marine 4 need a Class I or II vapor retarder on the inside, with exceptions; newer editions changed the details. Open-cell foam isn't one, so DOE recommends vapor-retarder primer or paint on the drywall. Closed-cell foam at about 2 inches tests under 1 perm in DOE's guide; check the product's data sheet.
3. Sealed attics (IRC R806.5). Per DOE/PNNL's summary of the 2018 IRC, no Class I vapor retarder may go on the attic floor side, and in zones 5 through 8 foam under the roof deck has to be a Class II vapor retarder or carry a Class II coating, which means vapor-retarder paint on open-cell. For foam-plus-loose-fill roofs, the foam layer must reach at least R-5 in zones 1 through 3 and more in colder zones; our spray foam guide by climate zone lists it by zone. In humid zones, also ask how the attic air will be kept dry once it is sealed.
4. Blowing agents. Since January 1, 2025, EPA rules (40 CFR 84.54) bar making or importing rigid polyurethane spray foam that uses an HFC, or an HFC blend, with a global warming potential of 150 or more. Selling or distributing such products is barred from January 1, 2028, three years later. Ask the bidder which product they spray and for its data sheet.
5. Thickness per pass. Closed-cell foam goes on 2 to 3 inches per pass, so a 7-inch roof deck is several passes. Ask how the bidder handles that on the schedule.
6. Minimum charges. Small jobs such as rim joists hit a $1,000 to $2,000 or more minimum at most companies, per HomeGuide.
7. Tax credit. The federal 25C credit doesn't apply to foam installed in 2026. The IRS says it is not allowed for property placed in service after December 31, 2025. Local utility rebates still exist; see our 2026 insulation rebate tracker.

Sources: U.S. DOE Building America, "Which Spray Foam Is Right For You?" (CARB / Steven Winter Associates, 2009); ICC, 2009 IRC Q&A, Section R316.5.3 Attics (PDF); DOE/PNNL Building America Solution Center, Double Wall Framing Code Compliance Brief (quotes IRC R702.7); DOE/PNNL Building America Solution Center, Controlling Moisture in Unvented Attics, Code Compliance Brief; DOE/PNNL Building America Solution Center, Below Deck Spray Foam Insulation for Existing Roofs; eCFR, 40 CFR 84.54, Restrictions on the use of hydrofluorocarbons; HomeGuide, "How Much Does Spray Foam Insulation Cost? (2026)" (Dec 1, 2025); IRS, FAQs on Public Law 119-21 changes to 25C and related credits.

Choose open-cell or closed-cell

Choose open-cell spray foam if:

• The foam stays above grade and dry, such as a 2x6 wall or a roof deck in a dry climate.
• You want the lowest price per board foot and have the depth to reach your R target.
• Your roof is older and you want foam that dries out after a leak. DOE notes that a leak under closed-cell foam can be hard to find.
• You're in climate zones 1 to 4, where the 2018 IRC (per DOE/PNNL) doesn't call for a vapor-retarder coating on roof-deck foam.

Choose closed-cell spray foam if:

• The foam goes on a crawl space wall, basement wall or rim joist.
• The area sits below the flood elevation in a mapped flood zone.
• The cavity is shallow, like a 2x4 wall that needs R-13.
• You need a vapor retarder from the insulation itself, as in a zone 5 to 8 roof deck or wall.
• You need R-38 or more at a roof deck within the thickness limits.

Getting bids that compare cleanly

Ask every bidder to write the foam type, inches, square footage and resulting R-value for each area, plus who supplies the thermal or ignition barrier. Then hold each line up against the cost-per-R row above. Our quote checker runs the board-foot math on a bid you already have, and you can request up to 3 quotes here.

Local cost pages for the seven metros we price: Phoenix, Tucson, Atlanta, Houston, Tampa, Nashville and Colorado Springs.

Get up to 3 spray foam quotes, open-cell or closed-cell

ZIP code

Continue

Open-cell vs closed-cell FAQ

Is closed-cell spray foam worth the higher price?

Per board foot, closed-cell costs about twice as much. Per unit of R-value, Angi's 2026 ranges put it within a few cents of open-cell ($0.18 to $0.46 against $0.17 to $0.44 per R per square foot). It earns its price where you need moisture control or a high R-value in a thin cavity.

Do I need a vapor retarder over open-cell spray foam?

In climate zones 5 through 8, usually yes. Under a sealed roof deck, the 2018 IRC (as summarized by DOE/PNNL) calls for a Class II vapor retarder or coating, so open-cell gets vapor-retarder paint. For frame walls, the IRC text DOE/PNNL quotes calls for a Class I or II vapor retarder on the inside in zones 5 to 8 and Marine 4; newer editions changed the details, so ask your building department which edition it enforces.

Can open-cell spray foam go in a crawl space?

DOE's Building America guide rates open-cell "not acceptable" for foundations and below-grade spaces, and FEMA's flood bulletin lists open-cell plastic foams as unacceptable below the flood elevation. Closed-cell is the usual choice there.

Can I combine the two foams?

Yes. DOE's guide expects most closed-cell wall jobs to be hybrids: a closed-cell layer against the sheathing with other insulation behind it. It suggests at least 1½ inches of closed-cell in a cold-climate hybrid wall, and 2 inches above 6,000 heating degree days. Under a sealed roof deck, the IRC sets the minimum R-value of the foam layer by climate zone.