Spray foam vs fiberglass vs cellulose: cost, R-value and where each belongs (October 2026)

Prices and regulation sources checked October 21, 2026.

Fiberglass and cellulose cost far less than spray foam for the same R-value, and spray foam is the only one of the three that also seals air. On our sample house, R-38 on a 1,600 square foot attic floor prices at $1,300 to $2,400 blown in and $1,800 to $5,300 in fiberglass batts, against $10,100 to $27,700 in spray foam. Per R-value per square foot, that works out to about 2 to 9 cents for the fibers and 17 to 46 cents for foam.

The price gap narrows where depth is short or water is likely. A 2x4 wall, a roof deck, a crawl space or a floor below the flood line is where foam's R-value per inch and moisture tolerance start to earn their price. Each total below is our arithmetic on published national rates, with rates and method stated.

The three materials, criterion by criterion

One cell in that table comes with a caveat. TVA EnergyRight's insulation pages don't say whether spray foam qualifies for its rebates, so ask before you count on one.

Sources: Profoam product price sheet (R-value per inch column); U.S. DOE Building America, "Which Spray Foam Is Right For You?" (2009); DOE Energy Saver (archived 2011), "Blanket (Batt and Roll) Insulation"; DOE/PNNL Building America Solution Center, Loose-Fill Insulation tool (table cites DOE, "Loose-Fill Insulations," May 1995); TVA EnergyRight, Home insulation & air sealing; FEMA, NFIP Technical Bulletin 2, Flood Damage-Resistant Materials Requirements (January 2025); eCFR, 16 CFR Part 1209 (CPSC cellulose insulation standard); ENERGY STAR, Choosing the Appropriate Insulation Type; Angi, "How Much Does Spray Foam Insulation Cost? [2026 Data]" (updated Sep 9, 2026); HomeGuide, "How Much Does Blown-in Insulation Cost? (2026)" (Nov 5, 2025).

What the cost guides publish

The job table below uses HomeGuide's blown-in rates because HomeGuide ties each price to an R-value; its R-38 attic row works out to $0.84 to $1.50 per square foot. Angi's range for blown-in is higher, at $1.75 to $7.50 per square foot (Angi, "How Much Does Blown-In Insulation Cost? [2026 Data]," updated Sep 24, 2026). If an estimate lands near Angi's figures, ask for the R-value, settled thickness and bag count in writing (see fine print item 1).

Sources: Angi, "How Much Does Spray Foam Insulation Cost? [2026 Data]" (updated Sep 9, 2026); Angi, "How Much Does Insulation Installation Cost? [2026 Data]" (updated Oct 6, 2026); Angi, "How Much Does Blown-In Insulation Cost? [2026 Data]" (updated Sep 24, 2026); HomeGuide, "How Much Does Spray Foam Insulation Cost? (2026)" (Dec 1, 2025); HomeGuide, "How Much Does Batt & Roll Insulation Cost? (2026)" (Nov 5, 2025); HomeGuide, "How Much Does Blown-in Insulation Cost? (2026)" (Nov 5, 2025); HomeGuide, "How Much Does Insulation Cost? (2026)" (Dec 19, 2025).

One house, priced three ways

The sample house is the same invented house as on our open-cell vs closed-cell page. It is not an average home:

• Attic floor: 1,600 sq ft, vented attic, existing insulation removed or absent.
• Exterior walls: 1,200 sq ft after subtracting openings.
• Spray foam: the open-cell low to the closed-cell high from that page, which shows the math.
• Fiberglass and cellulose: area × HomeGuide's installed price for that R-value.
• Figures are to the closest $100 and exclude removal of old material, air sealing and minimum fees.

Depths for loose-fill fiberglass and cellulose at R-38 come from DOE's loose-fill table (14 to 17 inches and 10 to 12 inches). The batt depth comes from HomeGuide's R-38 row.

Notes on that table:

• Per R-value, the fibers cost a fraction of foam. On the R-38 attic, blown-in works out to $0.022 to $0.039 per R per square foot and batts to $0.029 to $0.087. Foam runs $0.17 to $0.44 (open-cell) and $0.18 to $0.46 (closed-cell).
• Walls narrow the gap. In an open 2x4 wall, R-13 batts cost $0.05 to $0.16 per R per square foot, against foam's 17 to 46 cents. Foam's case there is air sealing and moisture control, not price.
• Small blown-in jobs hit minimums. HomeGuide says some companies have a $1,500 to $2,000 minimum for blown-in work. At R-30 this attic prices at $1,100 to $1,900, under that floor.
• HomeGuide's blown-in tables don't name the material, so the fiberglass and cellulose columns share one rate. HomeGuide's per-material rates ($1.00 to $2.80 fiberglass, $1.20 to $2.80 cellulose) suggest cellulose runs slightly higher at the low end.

What goes into each material

DOE/PNNL says cellulose is made from recycled newspaper and boxes, "usually manufactured locally," and the favored loose fill in DOE-funded low-income weatherization programs. It says about 20 to 40 percent of fiberglass sold as insulation is recycled. Settled density runs 1.5 to 2.0 pounds per cubic foot for loose cellulose and 0.5 to 1.0 for loose fiberglass, which is why the cellulose layer weighs more on a ceiling.

Batts vary by density. The DOE Energy Saver (archived 2011) table lists a standard 3½-inch fiberglass batt at R-11, a 3⅝-inch batt at R-13 and a high-density 3½-inch batt at R-15. HomeGuide says 2x4 framing fits up to R-15 and 2x6 framing up to R-23 with blown-in fill.

Sources: DOE/PNNL Building America Solution Center, Loose-Fill Insulation tool (table cites DOE, "Loose-Fill Insulations," May 1995); DOE Energy Saver (archived 2011), "Blanket (Batt and Roll) Insulation"; HomeGuide, "How Much Does Blown-in Insulation Cost? (2026)" (Nov 5, 2025).

Loose fill or batts on an attic floor

Loose fill covers an uneven attic floor better, and batts are the easier material to lay by hand. DOE/PNNL says loose fill "will cover the surfaces well without voids or gaps, is inexpensive to install, and is readily available." HomeGuide calls batts in an attic "DIY-friendly but is typically less effective than blown-in insulation that better fills gaps and oddly shaped areas." ENERGY STAR says "Laying fiberglass rolls is easiest for a DIY job," while loose fill "requires the use of a blowing machine."

Measure what is already up there

ENERGY STAR's quick check: if the insulation is "level with or below the attic floor joists, you probably need to add more insulation." If the insulation is "well above" the joists, "you probably have enough, and adding more insulation may not be cost-effective." To estimate what you have, multiply measured inches by its factors: 2.5 for loose fiberglass, 2.8 for rock wool, 3.7 for cellulose, 3.2 for fiberglass batts and 2.7 for vermiculite or perlite. By that rule, 4 inches of old loose fiberglass is about R-10. ENERGY STAR warns that vermiculite "may contain asbestos" and says not to disturb it until an approved lab has tested it.

ENERGY STAR also notes that "sometimes there is enough insulation in the middle of the attic and very little along the eaves," so measure in several spots.

Seal leaks before adding insulation

"EPA recommends air sealing the attic before adding attic insulation," per ENERGY STAR, whose air sealing guide says to "Plug the big holes first." It says leakage is likely greatest where walls meet the attic floor, at dropped soffits, and behind or under kneewalls. Darkened insulation marks a leak, because it has been filtering dusty house air. The guide pairs caulk with holes of ¼ inch or less and expanding foam with gaps from ¼ inch to 3 inches. Around flues it calls for aluminum flashing and high-temperature caulk ("Do not use spray foam"), and it notes that codes usually require 1 inch of clearance from metal flues and 2 inches from masonry chimneys. For open stud cavities behind kneewalls and in dropped soffits, it folds a 16-inch piece of unfaced fiberglass batt into a 13-gallon plastic garbage bag and stuffs it in, then covers the soffit with reflective foil or rigid foam board set in caulk or adhesive. HomeGuide says some contractors include air sealing in an insulation estimate, so ask. EPA estimates homeowners save an average of 15% on heating and cooling costs by air sealing their homes and adding insulation in attics, floors over crawl spaces and basements, and ENERGY STAR says attic insulation combined with air sealing can help reduce ice dams in winter.

ENERGY STAR advises calling a professional first if you find wet or damp insulation, moldy or rotted framing, kitchen, bath or dryer vents exhausting into the attic, little or no ventilation, or knob and tube wiring (pre-1930). It adds that sealing can cause naturally venting combustion appliances to back-draft, so have them tested before and after. Sealing "may trap indoor air pollutants such as carbon monoxide, radon and volatile organic compounds," and EPA recommends a radon test kit after reducing air leaks.

Adding batts over old insulation

ENERGY STAR rates an attic insulation job "Moderate − Difficult" for a homeowner, at 1 to 3 days, against 1 to 2 days for a contractor. Its gear list runs to safety glasses, gloves, a dust mask, a disposable coverall, kneepads and boards to walk on. It says to step on joists or truss chords, not exposed ceiling drywall, and to watch for roofing nails.

ENERGY STAR says the new layer doesn't have to match the old one: loose fill can go over batts, and batts over loose fill if they are "unfaced." Lay a second batt layer perpendicular to the first to cover the joist tops, working from the perimeter toward the attic opening. Keep insulation off soffit vents and at least 3 inches from recessed lights unless they are rated IC (Insulated Ceiling), using sheet metal or wire mesh as a barrier. HomeGuide warns that compression "reduces the air pockets and lowers the material's R-value," and puts soffit baffles at $2 to $3 each.

HomeGuide separates the two fiberglass forms: batts are pre-cut pieces, while rolls come 20 to 40 feet long and are cut to length on site. It says faced batts are "typically used for first-time applications" and unfaced material is the one to use "when increasing the attic insulation." Foil-faced batts are combustible and belong only in non-exposed spots. Its advice for handling fiberglass is to protect your eyes and skin from irritation and to wear a dust mask.

When the old layer has to come out

HomeGuide prices attic insulation removal at $1 to $2 per square foot, which is $1,600 to $3,200 on our 1,600 sq ft sample attic. It says to remove old insulation with fire, water or pest damage, or hazardous material, and notes that removal "exposes the area to seal all penetrations." It also recommends a $40 to $150 pest inspection before insulating. For a DIY top-up, HomeGuide puts 5 inches of loose fill over 1,000 square feet at $200 to $650.

Blowing loose fill to the right depth

DOE/PNNL says to install loose fill at the maker's recommended density and not to "fluff" it. Fluffed fill uses fewer bags, lets air move through it more easily and "leads to excessive settling," and "Fiberglass insulation is easier to fluff than cellulose or rock wool." Count the empty bags and compare that count with the coverage chart on the bag label (fine print item 1). By our math on DOE/PNNL's settled R per inch, R-49 takes about 13 to 15 settled inches of cellulose or 18 to 22 of loose fiberglass.

Rock wool is the third common loose fill. DOE/PNNL says it is spun from blast-furnace slag, settles 2 to 4 percent like fiberglass, rates R-3.0 to R-3.3 per inch settled and needs 11.5 to 13 inches for R-38. It calls rock wool the least common of the three.

Sources: ENERGY STAR, Attic Insulation Project; ENERGY STAR, Attic Air Sealing Project; ENERGY STAR, What to Look For: DIY Checks and Inspections; ENERGY STAR, Rule Your Attic!; DOE/PNNL Building America Solution Center, Loose-Fill Insulation tool (table cites DOE, "Loose-Fill Insulations," May 1995); HomeGuide, "How Much Does Attic Insulation Cost? (2026)" (Jan 13, 2026); HomeGuide, "How Much Does Batt & Roll Insulation Cost? (2026)" (Nov 5, 2025).

Scenarios where fiberglass or cellulose is the better buy

Sources: ENERGY STAR, What to Look For: DIY Checks and Inspections; ENERGY STAR, Attic Insulation Project; HomeGuide, "How Much Does Attic Insulation Cost? (2026)" (Jan 13, 2026); DOE/PNNL Building America Solution Center, Loose-Fill Insulation tool (table cites DOE, "Loose-Fill Insulations," May 1995).

Where each one wins

Vented attic floor

Fiberglass and cellulose win on price. DOE's spray foam guide says open-cell foam's R-value per inch is "not much higher than far less expensive choices such as cellulose and fiberglass," and it prefers a thin closed-cell air-sealing layer rather than full-depth foam on an attic floor. Pairing loose fill with separate air sealing still costs $1,700 to $5,400 on the sample house. Between the two fibers, DOE/PNNL's table gives cellulose the shorter depth at R-38, 10 to 12 inches against 14 to 17. The same table lists cellulose as heavier, at 1.25 to 2.0 pounds per square foot at R-38, and marks it "No" for ½-inch drywall at 24 inches on center, where fiberglass gets a "Yes".

Sealed attic at the roof deck

At the roof deck the decision is open-cell or closed-cell foam, and our open-cell vs closed-cell page covers it, including IRC R806.5. The Phoenix and Atlanta cost pages price local roof decks.

Closed exterior walls

To see whether a finished wall is empty, ENERGY STAR suggests shutting off power to an outlet, confirming it with a voltage tester, removing the cover and shining a flashlight into the crack around the box. Check outlets on every floor and in old and new parts of the house. Blown fiberglass and dense-pack cellulose go in through drilled holes. HomeGuide prices dense-pack at $1.60 to $4.20 per square foot and recommends a pro, or measuring and weighing the fill, so it reaches 3.5 pounds per cubic foot. TVA EnergyRight says that where wall gaps can't be reached, "dense pack insulation (cellulose or fiberglass) or blown-in foam insulation will provide an adequate level of air sealing."

Open walls in a remodel or new build

Batts are cheapest. ENERGY STAR rates batts at a "Basic" skill level, the lowest it lists. Spray foam costs more but seals the cavity, and closed-cell reaches R-13 in under 2 inches of a 2x4 wall.

Crawl spaces, basements and flood zones

FEMA's flood-zone ratings for all three are in the criteria table above. Its acceptable row names sprayed polyurethane foam without a cell type, so ask the local floodplain office. DOE's spray foam guide rates closed-cell "preferred" for foundations and below-grade spaces. Our Houston and Nashville cost pages price local crawl spaces.

Weight-limited ceilings

DOE/PNNL says cellulose "is not recommended for use in mobile home ceilings or floors" because of its weight, and that fiberglass may be used there.

Sources: U.S. DOE Building America, "Which Spray Foam Is Right For You?" (2009); DOE/PNNL Building America Solution Center, Loose-Fill Insulation tool (table cites DOE, "Loose-Fill Insulations," May 1995); TVA EnergyRight, Home insulation & air sealing; HomeGuide, "How Much Does Blown-in Insulation Cost? (2026)" (Nov 5, 2025); ENERGY STAR, Choosing the Appropriate Insulation Type; FEMA, NFIP Technical Bulletin 2, Flood Damage-Resistant Materials Requirements (January 2025).

Fine print before you sign

1. Get the receipt the FTC requires (16 CFR 460.17). Installers must give you a contract or receipt. For loose fill it must show the coverage area, initial installed thickness, minimum settled thickness, R-value and number of bags. For other insulation, including batts and foam, it must show coverage area, thickness and R-value. Loose-fill bag labels must chart minimum settled thickness and bags per 1,000 square feet at R-13, 19, 22, 30, 38 and 49 (16 CFR 460.12). The receipt must be "dated and signed by the installer," list each part of the house separately and not add up coverage areas or R-values across parts. The rule also says "Do not multiply the R-value for one inch by the number of inches you installed." Before you agree to buy, an installer must show you the manufacturer's fact sheet for that insulation (16 CFR 460.15), which carries a boxed "READ THIS BEFORE YOU BUY" notice (460.13).
2. Loose fill settles. DOE/PNNL puts loose-fill cellulose at 10 to 20 percent settling and loose-fill fiberglass at 2 to 4 percent. Ask whether the quoted R-value is at installed or settled thickness.
3. Cellulose fire rules (16 CFR Part 1209). CPSC's interim standard requires consumer cellulose insulation made after October 15, 1979 to pass corrosiveness, critical radiant flux and smoldering combustion tests. Every container must carry the statement "This product meets the amended CPSC standard for flame resistance and corrosiveness of cellulose insulation." Check the bag.
4. Foam needs a fire covering (IRC R316). Per DOE's spray foam guide, the IRC requires a thermal or ignition barrier over foam. Ask whether the foam price includes that covering.
5. Spray foam blowing agents. The federal rule on HFC blowing agents in spray foam (40 CFR 84.54) is covered on our open-cell vs closed-cell page.
6. No federal money in 2026. The IRS says the 25C credit "will not be allowed for any property placed in service after December 31, 2025," whatever the material. Local programs are listed on our rebate tracker, and ENERGY STAR notes that a state's Weatherization Assistance Program (WAP) may offer financial help with air sealing and insulating.

Sources: eCFR, 16 CFR Part 460 (FTC R-value Rule; 460.12, 460.13, 460.15, 460.17); DOE/PNNL Building America Solution Center, Loose-Fill Insulation tool (table cites DOE, "Loose-Fill Insulations," May 1995); eCFR, 16 CFR Part 1209 (CPSC cellulose insulation standard); U.S. DOE Building America, "Which Spray Foam Is Right For You?" (2009); ICC, 2009 IRC Q&A on R316.5.3 Attics; HomeGuide, "How Much Does Blown-in Insulation Cost? (2026)" (Nov 5, 2025); IRS, 25C guidance under P.L. 119-21; ENERGY STAR, Attic Insulation Project.

Choose spray foam, fiberglass or cellulose

Choose spray foam if:

• You are sealing the attic at the roof deck.
• The area is a crawl space, basement wall or rim joist, or sits below the flood elevation (closed-cell).
• The cavity is shallow and needs its R-value in under 2 inches, like a 2x4 wall at R-13.
• You want the insulation to be the air seal and won't pay for separate air sealing.

Choose fiberglass if:

• You are filling open wall or floor cavities with batts, the cheapest wall option on our sample house.
• You want to do it yourself. ENERGY STAR rates batts "Basic."
• The ceiling framing or drywall can't carry heavier fill, per DOE/PNNL's weight table.

Choose cellulose if:

• You are topping up a vented attic floor and want the shorter depth at R-38 (10 to 12 inches against 14 to 17 for loose-fill fiberglass).
• The walls are closed and you want dense-pack fill through drilled holes.
• You will also pay for attic air sealing, since loose fill alone doesn't stop air leakage.

Comparing bids across materials

Have every estimate name the material, R-value, inches (installed and settled, for loose fill) and area for each part of the house, and say whether air sealing is in the price. Test a foam estimate against published rates, or ask for local estimates.

Local cost pages: Phoenix, Tucson, Atlanta, Houston, Tampa, Nashville, Colorado Springs, Huntsville and Tulsa.

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Spray foam vs fiberglass vs cellulose FAQ

Is spray foam worth it over blown-in cellulose in an attic?

On price alone, rarely on a vented attic floor. On our sample house, R-38 blown in costs $1,300 to $2,400, and $1,700 to $5,400 with separate air sealing, against $10,100 to $27,700 for foam. Foam makes more sense when the attic is being sealed at the roof deck.

Does cellulose settle more than fiberglass?

Yes. DOE/PNNL figures put loose-fill cellulose at 10 to 20 percent settling and loose-fill fiberglass at 2 to 4 percent. FTC rules make installers list the minimum settled thickness on loose-fill receipts.

Which insulation can go below the flood line?

FEMA's Technical Bulletin 2 rates "Sprayed polyurethane foam (SPUF) or closed-cell plastic foams" acceptable. It rates fiberglass, cellulose and open-cell plastic foams unacceptable. Ask your local floodplain office before foam goes below the flood elevation.

Can I install fiberglass or cellulose myself?

ENERGY STAR rates batts "Basic" and loose fill "Intermediate." Its sprayed-foam category is "Advanced (Certified Installer Needed)." Angi notes blowers rent for under $100 a day but says getting the loft and placement right "is genuinely difficult."