By The Roofing Brief Team. Last reviewed: October 2026.
The best insulation for an attic follows your attic type and climate zone, not one material winning every time. For a standard vented attic floor, blown-in cellulose is the best overall value: it reaches R-49 at 14.3 inches installed (Greenfiber SANCTUARY chart), and HomeWyse prices it installed at $1.67 to $2.92 per sq ft in May 2026, about $1,670 to $2,920 for 1,000 sq ft. For a conditioned, unvented roofline or a leaky older home in Zones 5 to 8, closed-cell spray foam wins on R-6 to R-6.5 per inch and its built-in air seal, at a higher price.
Our companion reference, the attic ventilation guide, covers the airflow side. Here the decision is which insulation fits your attic type, ENERGY STAR climate zone, budget and skill level.
What is the best insulation for an attic overall?
For most homes, blown-in cellulose is the best attic insulation by value. It delivers about R-3.7 per inch on Greenfiber’s SANCTUARY chart (R-49 at 14.3 in installed, 13.3 in settled), costs less per 1,000 sq ft at R-49 than Owens Corning AttiCat fiberglass in our October 19, 2026 bag-price check (worked example below), and settles into gaps around junction boxes and top plates that batts leave open. The pick changes only when the attic becomes conditioned space, sits in Zones 5 to 8 with heavy air leakage, or has to be done by hand with batts.
Use the decision table first; the sections after it give the spec sheet behind each verdict.
| Your situation | Best pick | Why it wins here |
|---|---|---|
| Standard vented attic floor, any budget | Blown-in cellulose | About R-3.7 per inch; $1.67 to $2.92 per sq ft installed (HomeWyse, May 2026) |
| Tight budget, willing to DIY | Blown-in cellulose or AttiCat fiberglass | About 71 SANCTUARY bags or 25 AttiCat bags cover 1,000 sq ft at R-49 |
| Cold climate (Zone 5 to 8), leaky older home | Closed-cell spray foam, or air sealing plus R-60 cellulose | R-6 to R-6.5 per inch plus air seal in the least depth |
| Converting attic to conditioned space (HVAC or storage) | Spray foam at the roofline | Unvented assembly under IRC R806.5; no soffit venting needed |
| Hot climate (Zone 1 to 3), existing partial insulation | Top up with blown-in, add a radiant barrier if ducts are in the attic | FSEC measured 9% cooling savings from radiant barriers in Florida homes |
| Cathedral or low-slope ceiling with no attic | Closed-cell spray foam | High R per inch fits shallow rafter bays without venting |
Best attic insulation by type, ranked
Ranked by how often it is the right call, attic insulation orders as blown-in (loose-fill) cellulose first, closed-cell spray foam second, blown-in fiberglass third, open-cell foam fourth and fiberglass batts last. Loose-fill is the blown-in category: cellulose made to ASTM C739 or fiberglass made to ASTM C764, installed with a blowing machine rather than in pre-cut batts.
| Rank | Type | R-value per inch | Best for | Verdict |
|---|---|---|---|---|
| 1 | Blown-in (loose-fill) cellulose | About R-3.7 | Standard vented attic floors, any budget | Best value, self-seals around framing |
| 2 | Closed-cell spray foam | R-6.0 to R-6.5 | Conditioned rooflines, cold leaky homes, shallow bays | Highest R per inch, doubles as an air barrier |
| 3 | Blown-in (loose-fill) fiberglass | About R-2.9 (AttiCat: R-49 at 17 in) | DIY jobs, lighter loads on older framing | Cheap and fast, needs more depth |
| 4 | Open-cell spray foam | R-3.5 to R-3.7 | Interior rooflines in mild, dry climates | Cheaper foam, not a vapor barrier |
| 5 | Fiberglass batts | About R-2.9 to R-3.7 | Small, open, obstruction-free attics | Lowest sticker price, gaps cut real R-value |
For R per inch across all materials, see the highest R-value insulation guide, which ranks polyiso, XPS and mineral wool boards that rarely reach an attic floor.
How much insulation does an attic actually need?
Most US attics should reach R-49, and Zones 4 through 8 target R-60. The ENERGY STAR recommended R-values are R-30 for an uninsulated attic in Zone 1, R-49 in Zones 2 and 3, and R-60 in Zones 4 through 8; if the attic already has 3 to 4 inches, add R-25, R-38 and R-49 for the same zones. Those match the 2021 IECC prescriptive ceiling values of R-30, R-49 and R-60.
Depth decides fit. R-49 takes 14.3 inches of blown-in cellulose (settling to 13.3 inches) on the Greenfiber SANCTUARY chart, 17 inches of AttiCat fiberglass on Owens Corning’s AttiCat data sheet (Pub. No. 10011273-L, May 2026), but only about 7.5 to 8 inches of closed-cell spray foam at R-6 to R-6.5 per inch. In a shallow attic or a cathedral bay, that depth gap often decides the material before price does.
| Climate zone | Recommended attic R-value | Cellulose depth for target | AttiCat fiberglass depth | Closed-cell foam depth |
|---|---|---|---|---|
| Zone 1 (far south) | R-30 | ~8.9 in | ~10.75 in | ~5 in |
| Zones 2 to 3 | R-49 | ~14.3 in | ~17 in | ~7.5 to 8 in |
| Zones 4 to 8 | R-60 | ~17.3 in | ~20.5 in | ~9.5 to 10 in |
Sources: ENERGY STAR, Recommended Home Insulation R-Values (uninsulated attic column); Greenfiber SANCTUARY coverage chart DM-6.3-38 Rev F (initial installed thickness); Owens Corning AttiCat PINK data sheet 10011273-L. Foam depth is Roofing Brief arithmetic at R-6 to R-6.5 per inch; use the product’s own data sheet.
Worked example: bags, depth and cost for a 1,000 sq ft attic
Both makers print FTC-required coverage charts (16 CFR 460.12) listing bags per 1,000 sq ft, so the DIY material math is exact. Prices are Google Shopping listings checked October 19, 2026: SANCTUARY 25 lb bags at $13.99 (Prosource Insulation) to $16.99 (The Lumberyard), and AttiCat 27.5 lb bags at $62.00 (Home Depot).
| Goal | SANCTUARY cellulose | AttiCat fiberglass | Source |
|---|---|---|---|
| R-30 from bare drywall | 38.6 bags, 8.9 in installed: about $540 to $656 | 14.6 bags, 10.75 in: about $905 | Greenfiber chart; OC 10011273-L |
| R-49 from bare drywall | 70.8 bags, 14.3 in installed: about $990 to $1,203 | 25 bags, 17 in: about $1,550 | Greenfiber chart; OC 10011273-L |
| R-60 from bare drywall | 86.0 bags, 17.3 in installed: about $1,203 to $1,461 | 31.5 bags, 20.5 in: about $1,953 | Greenfiber chart; OC 10011273-L |
| Top up existing R-19 (about 6 in old batts) to R-49 | Add R-30: 38.6 bags, 8.9 in: about $540 to $656 | Add R-30: 14.6 bags, 10.75 in: about $905 | Greenfiber worked example uses R-19 for 6 in batts |
Roofing Brief arithmetic: bags x listed price, rounded. Greenfiber says job conditions can move actual coverage by as much as 10 percent and that both the minimum bag count and the minimum installed thickness must be met to claim the R-value. Installed by a contractor, HomeWyse’s May 2026 cellulose estimate of $1.67 to $2.92 per sq ft includes vent baffling at the soffits.
Blown-in cellulose vs blown-in fiberglass: which is better?
For a vented attic floor, blown-in cellulose edges out blown-in fiberglass on R-value per inch and air resistance, while fiberglass is lighter. Cellulose runs about R-3.7 per inch on Greenfiber’s chart; AttiCat reaches R-49 at 17 inches, about R-2.9 per inch. In bag weight, R-49 is 1.77 lb per sq ft of SANCTUARY versus 0.688 lb per sq ft of AttiCat, which matters on older ceiling framing.
The trade-offs split three ways. Cellulose is recycled newsprint treated for fire and pest resistance, and Greenfiber rates its settled thickness at 90 percent of installed, which installers handle by blowing to the chart’s initial installed depth. AttiCat’s chart lists the same initial and settled thickness, so no settling allowance. Oak Ridge National Laboratory tests in its Large Scale Climatic Simulator, reported in Energy Design Update (October 1991), found an older cubed loose-fill fiberglass lost R-value to air convection at large indoor-outdoor temperature differences; makers later changed the product, so check current data sheets for cold-attic use.
Batt insulation for attics: fiberglass and mineral wool
Batt insulation is the right attic choice only for small, open, obstruction-free bays where batts lie flat between joists without gaps. Fiberglass batts run R-19 at 6.5 in to R-49 at 14 in on Owens Corning’s PINK Next Gen submittal (Pub. No. 10024913), about R-2.9 to R-3.7 per inch for attic batts, and mineral wool runs higher: ROCKWOOL Comfortbatt is R-30 at 7.25 in and R-38 at 9.5 in on its US technical data sheet (issued 07-2026). HomeGuide’s 2026 batt guide puts installed batts at $0.80 to $2.60 per sq ft.
Attic batts are rated by thickness, so the label maps to a nominal R-value before any compression or gaps. Owens Corning lists standard fiberglass attic batts up to R-49 at 14 inches; mineral wool reaches a given R-value in less depth because it is denser. The chart below shows the nominal R-value each common batt thickness delivers.
| Batt thickness | Fiberglass R-value | Mineral wool R-value | Typical use |
|---|---|---|---|
| 3.5 in | R-11 to R-15 | R-15 | 2×4 bay, first floor layer |
| 5.5 in | R-20 to R-21 | R-23 | 2×6 bay, single-layer minimum |
| 6.5 to 7.25 in | R-19 (6.5 in); R-22 (6.75 in) | R-30 (7.25 in) | Deeper joists or top-up layer |
| 9.5 in | R-30 | R-38 | Single layer between deep joists |
| 12 in | R-38 | Not listed | Near a full attic target in one pass |
| 14 in | R-49 | Not listed | Full R-49 in one unfaced layer, if joists allow |
Sources: Owens Corning PINK Next Gen submittal sheet, Pub. No. 10024913; ROCKWOOL Comfortbatt technical data sheet (US, issued 07-2026). Thicknesses are nominal label values.
Reaching R-49 with batts usually means two layers, because an R-49 batt is 14 inches thick and a 2×8 ceiling joist is 7.25 inches deep. The standard method is an R-30 layer (9.5 in fiberglass or 7.25 in Comfortbatt) between the joists and a second R-19 layer (6.5 in) laid crosswise over them to cover the wood and cut thermal bridging. Mineral wool gets there in less depth but costs more per square foot.
Batts vs blown-in for an attic floor: choose batts for new construction with open joist bays at 16 or 24 in on center and a DIY installer who wants no blowing machine; choose blown-in to retrofit over existing insulation or on any floor with wiring, bracing, and irregular framing.
- Pick batts when the attic is new or gutted, the joists are open and standard-spaced, you want to lay material by hand, and you can cross-lay a 9.5 in R-30 layer and a 6.5 in R-19 layer to reach R-49.
- Pick blown-in when you are adding depth over existing insulation (8.9 in of SANCTUARY adds R-30), the attic floor has obstructions and penetrations, or you want loose fill to close the gaps batts leave along framing.
Mineral wool batts and rigid boards are ranked head to head in the highest R-value insulation guide.
When is spray foam the best attic insulation?
Spray foam is the best attic insulation when you are converting the attic to conditioned space, sealing a leaky older home in Zones 5 to 8, or fitting high R-value into shallow rafter bays. Closed-cell spray foam delivers R-6 to R-6.5 per inch, so about 7.5 to 8 in reaches R-49, and it creates its own air barrier. Open-cell foam is cheaper at R-3.5 to R-3.7 per inch but is not a vapor barrier and is usually kept out of cold, humid attics.
Spray foam is the wrong pick in three cases. In a vented attic in Zones 1 to 3, topping up blown-in to the ENERGY STAR target plus air sealing costs less: HomeGuide’s 2026 attic guide puts spray foam at $1.50 to $5.00 per sq ft against HomeWyse’s $1.67 to $2.92 for installed cellulose. When a foam quote is given per board foot (HomeGuide: $0.60 to $2.90), remember R-49 in closed-cell is about 7.5 board feet per sq ft. And a full-attic foam job needs a professional installer controlling ratio and temperature.
One structural note: foam on the roof deck creates an unvented, conditioned attic that must meet IRC R806.5, and IRC R316 covers ignition or thermal barriers over foam plastic. Before converting, check how it interacts with existing soffit vents, since a sealed roofline is designed to work without them.
What does each attic insulation type cost in 2026?
Named sources disagree, so compare quotes per sq ft at a stated R-value. HomeWyse puts installed blown-in cellulose at $1.67 to $2.92 per sq ft and blown-in attic insulation to R-45 with baffles at $3.75 to $7.77 (both May 2026); HomeGuide’s 2026 guides put blown-in at $1.00 to $2.80, batts at $0.80 to $2.60, and attic spray foam at $1.50 to $5.00 per sq ft. DIY cellulose to R-49 is about $990 to $1,203 in material for 1,000 sq ft (worked example above).
| Material | R-value per inch | Installed cost per sq ft (source, date) | Air seal on its own? | DIY-friendly? |
|---|---|---|---|---|
| Blown-in cellulose | About R-3.7 | $1.67 to $2.92 (HomeWyse, May 2026) | Partial | Yes |
| Blown-in, any fiber, to R-45 with baffles | About R-2.9 to R-3.7 | $3.75 to $7.77 (HomeWyse, May 2026) | No | Yes |
| Blown-in, general | About R-2.9 to R-3.7 | $1.00 to $2.80 (HomeGuide, 2026) | No | Yes |
| Fiberglass batts | About R-2.9 to R-3.7 | $0.80 to $2.60 (HomeGuide, 2026) | No | Yes |
| Spray foam, attic | R-3.5 to R-3.7 open; R-6.0 to R-6.5 closed | $1.50 to $5.00, or $0.60 to $2.90 per board foot (HomeGuide, 2026) | Yes | No |
The payback math often favors the cheaper material. ENERGY STAR says sealing and insulating can save up to 10 percent on annual energy bills, and a $1,670 to $2,920 cellulose job recovers that saving sooner than a foam job priced several times higher, unless the foam also fixes an air-leakage or ice-dam problem. For the same materials ranked by price per unit of R-value, see the cheapest attic insulation, ranked by cost per R. The federal 25C credit that covered insulation ended for property placed in service after December 31, 2025 under Public Law 119-21, though qualifying 2025 projects can still be claimed on a 2025 return (IRS 25C page); see whether roof and energy work is tax deductible for what still applies.
How do the materials hold up over time?
Longevity separates the materials as much as price does. Fiberglass batts lose effective R-value to gaps, compression and moisture, which is why the ANSI/RESNET/ICC 301 energy-rating standard grades installs I to III and penalizes gaps and voids in Grade III. Blown-in cellulose settles to 90 percent of installed depth, per Greenfiber, and then holds. Closed-cell spray foam does not settle.
So a cheaper batt job can cost more per year of real performance. A batt attic with gaps at every 2×6 joist and crushed edges at the eaves runs below its label R-value the whole time, while blown-in cellulose blown to its 14.3 in chart depth for R-49 still sits at 13.3 in after settling.
What goes wrong with attic insulation, and how do you avoid it?
The most common failure is insulating without air sealing first, which lets warm air bypass the insulation. ENERGY STAR’s attic guidance says contractors should seal air leaks in the attic floor before adding insulation; the usual leaks are at can lights, the hatch, plumbing stacks and interior wall top plates. Our step by step guide on how to insulate an attic puts that sealing first.
- Air seal first. Seal penetrations, the attic hatch, and top plates with fire-rated caulk or canned foam before any insulation goes in.
- Protect ventilation. Install eave baffles so blown-in material does not block soffit airflow; IRC R806.3 requires at least 1 in of air space at the vents.
- Keep clearances. Greenfiber’s instructions call for barriers at least 3 inches from recessed lights, flues and other heat sources; follow local code too.
- Hit the target depth. Staple depth rulers to joists so the installed height reaches the chart’s initial installed thickness, such as 14.3 in of SANCTUARY for R-49.
- Do not over-seal a vented attic. Blocking eave or ridge venting traps moisture and can cause condensation and mold.
Blocked ventilation from over-packed insulation causes winter moisture problems and ice dams. If your attic already has ice at the eaves, read the ice dam prevention methods that actually work before adding depth, because the fix is usually air sealing and balanced 1/150 or 1/300 venting under IRC R806.2, not more insulation alone. For how insulation fits a whole roof system by region, see our 2026 residential roofing guide.
Best attic insulation for hot climates
In a hot climate (ENERGY STAR Zones 1 to 3) the attic problem inverts: you are keeping roof heat out. The best attic insulation for hot climates is still loose-fill cellulose or fiberglass to the zone target, R-30 in Zone 1 and R-49 in Zones 2 and 3, with air sealing first, plus a radiant barrier where the ducts or air handler sit in the attic.
The Florida Solar Energy Center’s radiant barrier pilot (FSEC-CR-1231-01, January 2001) measured the trade-off. Across 8 retrofit homes, radiant barriers cut cooling energy by an average 3.6 kWh per day, about 9 percent, and summer afternoon peak demand by 420 watts, about 16 percent. In the same utility’s data, homes with R-30 attic insulation used 3.4 kWh per day less for cooling than homes with R-19, but cut peak demand by only 130 watts, about 5 percent.
| If your hot-climate attic has | Do this first | Evidence |
|---|---|---|
| R-19 or less of insulation | Top up to R-30 (Zone 1) or R-49 (Zones 2 and 3) | FSEC: R-30 homes used 3.4 kWh/day less for cooling than R-19 homes |
| Ducts or air handler in the attic | Add a radiant barrier with the top-up | FSEC: 420 W lower peak demand after radiant barrier retrofit |
| Already R-38 or more, ducts indoors | Air seal and fix ventilation; skip foam | ENERGY STAR targets already met in Zones 1 to 3 |
| Converting the attic to conditioned space | Open- or closed-cell foam at the deck | Unvented assembly under IRC R806.5 |
For Florida code minimums, product picks and more radiant barrier evidence, see our guide to the best attic insulation for Florida.
Frequently asked questions
What is the best insulation for an attic?
For most vented attic floors, blown-in cellulose is the best insulation on value: it reaches R-49 at 14.3 inches on Greenfiber’s SANCTUARY chart and costs $1.67 to $2.92 per sq ft installed in HomeWyse’s May 2026 estimate. Closed-cell spray foam, at R-6 to R-6.5 per inch, is the best pick for conditioned rooflines, cold-climate leaky homes, and shallow cathedral bays, at a higher price per sq ft.
What type of insulation is best for a cold climate attic?
In Zones 5 to 8, ENERGY STAR recommends R-60, which is 17.3 inches of SANCTUARY cellulose or 20.5 inches of AttiCat fiberglass. Closed-cell spray foam wins when the home is leaky or the attic is being conditioned, because its R-6 per inch plus built-in air seal fits in the least depth. In a sound vented attic, air sealing plus cellulose to R-60 delivers the same R-value for less.
Is spray foam or blown-in insulation better for an attic?
Blown-in is better for standard vented attic floors on cost: HomeWyse prices installed cellulose at $1.67 to $2.92 per sq ft (May 2026), while HomeGuide’s 2026 attic guide puts spray foam at $1.50 to $5.00 per sq ft at typical thickness. Spray foam is better for conditioned rooflines and shallow bays, where R-6 to R-6.5 per inch and an air seal matter more than price.
What kind of insulation is best for a DIY attic project?
Blown-in cellulose or AttiCat fiberglass with a borrowed or rented blower. For a 1,000 sq ft attic at R-49, the coverage charts call for 70.8 bags of SANCTUARY (about $990 to $1,203 at October 19, 2026 listings) or 25 bags of AttiCat (about $1,550 at a $62 Home Depot listing). Spray foam is not a DIY material for a full attic.
Are batts or blown-in insulation better for an attic floor?
Blown-in usually beats batts on an existing attic floor because it fills the gaps around joists, wiring, and cross-bracing that batts leave open. Batts make sense in new construction with open, evenly spaced joist bays. To reach R-49 with batts you typically stack two cross-laid layers, such as a 9.5 in R-30 layer topped by a 6.5 in R-19 layer. For cost, depth and install grading side by side, see our comparison of batts vs blown-in for an attic floor.
What is the best type of insulation for an attic?
Ranked by how often it is the right pick, blown-in (loose-fill) cellulose leads for standard vented attic floors (R-49 at 14.3 in), closed-cell spray foam leads for conditioned rooflines and cold leaky homes at R-6 to R-6.5 per inch, blown-in fiberglass suits DIY jobs at about R-2.9 per inch, and batts fit only small open attics.
What is the best attic insulation for hot climates?
Loose-fill cellulose or fiberglass to R-30 in Zone 1 or R-49 in Zones 2 and 3, after air sealing, plus a radiant barrier when ducts sit in the attic. The Florida Solar Energy Center measured about 9 percent cooling savings and 420 watts lower peak demand from radiant barrier retrofits in 8 Florida homes (FSEC-CR-1231-01).
Can you have too much attic insulation?
Yes, in effect. R-60 is the highest level ENERGY STAR’s table recommends, and each added inch saves less than the one before. The bigger risk is packing insulation so deep that it blocks soffit venting; IRC R806.3 requires at least 1 inch of air space at the vents. Install eave baffles that rise above the insulation so more depth does not create a ventilation problem.
How much does it cost to insulate an attic in 2026?
For a 1,000 sq ft attic, installed blown-in cellulose runs about $1,670 to $2,920 at HomeWyse’s May 2026 rate of $1.67 to $2.92 per sq ft, and DIY cellulose to R-49 about $990 to $1,203 in bags. The federal 25C tax credit for insulation ended for property placed in service after December 31, 2025, so 2026 projects no longer qualify, though some state and utility rebates still can.