Spray Foam vs Blown-In Insulation in 2026: Cost and Performance Comparison
Blown-in insulation costs $1.50 to $3.50 per square foot installed versus $3 to $7 per square foot for closed-cell spray foam in attic applications. Spray foam provides superior air sealing and a higher R-value per inch, but the spray foam vs blown-in insulation decision comes down to your primary goal: if you want maximum R-value and air sealing in one material (sealed attic, unvented roof deck), spray foam is worth the 2 to 4x cost premium. If you want to add R-value to an existing ventilated attic floor, blown-in with air sealing is more cost-effective.
The spray foam vs blown-in debate is one where the application location determines the answer more than the materials themselves. On an attic floor (insulating the ceiling below to keep conditioned air in the living space), blown-in with air sealing beats spray foam on cost with nearly equivalent performance. On a roof deck (insulating the underside of the roof sheathing to create a conditioned attic), spray foam is the right material because it simultaneously insulates and air-seals in a single pass without requiring separate venting. Understanding which application matches your project determines which material wins for your specific situation.
The attic insulation calculator compares blown-in and spray foam costs for your specific attic size and R-value target.
Open the Insulation Calculator →Spray Foam vs Blown-In Cost Per Square Foot in 2026
| Material | R-value per inch | Installed cost per sq ft | Cost to reach R-38 per sq ft |
|---|---|---|---|
| Blown-in fiberglass | R-2.2 to 2.7 | $1.50 to $3.00 | $1.50 to $3.00 (14-17 inches) |
| Blown-in cellulose | R-3.2 to 3.8 | $1.50 to $3.50 | $1.50 to $3.50 (10-12 inches) |
| Open-cell spray foam | R-3.5 to 3.8 | $1.00 to $2.00 | $3.50 to $8.00 (10-11 inches) |
| Closed-cell spray foam | R-6.0 to 7.0 | $3.00 to $7.00 | $16 to $38 (5.5-6.3 inches) |
Performance Comparison: Spray Foam vs Blown-In
| Characteristic | Closed-cell spray foam | Blown-in cellulose | Blown-in fiberglass |
|---|---|---|---|
| R-value per inch | Excellent (R-6.5) | Good (R-3.5) | Fair (R-2.5) |
| Air barrier capability | Excellent (full seal) | Poor (needs separate air sealing) | Poor (needs separate air sealing) |
| Moisture barrier | Excellent (Class II vapor retarder) | Poor (absorbs moisture) | Good (does not absorb moisture) |
| Cost efficiency to target R-value | Poor (highest material cost) | Excellent (lowest material cost) | Good (low material cost) |
| DIY installation | Poor (requires professional) | Excellent (rental machine available) | Excellent (rental machine available) |
| Structural reinforcement | Excellent (adds rigidity) | None | None |
| Pest resistance | Excellent (impervious) | Good (borate-treated) | Good (not a food source) |
| Settling over time | None | 15 to 20% settling | Minimal |
For the attic insulation cost guide that covers the full project including material selection, our attic insulation cost guide covers pricing by R-value and climate zone. For crawl space insulation that pairs with attic work, our crawl space encapsulation guide covers below-grade moisture and insulation.
Best Application for Each Insulation Type
When blown-in wins: ventilated attic floor
In a conventional vented attic (soffit vents plus ridge vent), the correct insulation strategy is to insulate the attic floor (ceiling of the living space below) and keep the attic ventilated. Blown-in fiberglass or cellulose on the attic floor, preceded by air sealing of all penetrations, achieves the DOE recommended R-value at the lowest cost. Adding closed-cell spray foam to achieve the same R-38 on an attic floor costs 5 to 10 times more than blown-in without proportionally better performance in a ventilated attic design. Blown-in is the clear winner for ventilated attic floor insulation.
When spray foam wins: unvented conditioned attic
An unvented (conditioned) attic places insulation at the roof deck (underside of the roof sheathing) rather than the attic floor. This makes the attic itself a conditioned space, which eliminates ductwork heat loss (if HVAC equipment is in the attic), improves ice dam resistance in cold climates, and eliminates attic ventilation requirements. Closed-cell spray foam applied to the underside of the roof deck is the correct material for this design because it simultaneously insulates, air seals, and acts as a vapor retarder, all in one pass. A minimum of 2 inches of closed-cell foam (R-13) at the roof deck is required by code in most climates before other insulation can be added; full unvented attic insulation typically uses 3 to 4 inches of closed-cell (R-19 to R-26).
20-Year Lifecycle Cost Comparison: 1,200 sq ft Attic
| Cost item | Blown-in cellulose + air seal | Closed-cell spray foam |
|---|---|---|
| Installation (1,200 sq ft) | $2,400 to $5,400 | $19,200 to $44,800 |
| Annual energy savings (Zone 5) | $380 to $520/year | $400 to $540/year |
| 20-year energy savings | $7,600 to $10,400 | $8,000 to $10,800 |
| Re-treatment needed? | Top-up at 15-20 yrs (cellulose settling): $300 to $600 | None |
| Net 20-year cost | $(1,200) to $2,100 net savings | $8,400 to $34,000 net cost |
The lifecycle comparison shows blown-in cellulose with air sealing pays for itself in energy savings within 5 to 14 years in Climate Zone 5. Closed-cell spray foam for the same ventilated attic floor does not pay back its installation premium in 20 years of energy savings. This is the definitive reason blown-in beats spray foam for ventilated attic floor insulation: the energy savings are nearly identical, but the cost is 5 to 10 times less.
Three Real Spray Foam vs Blown-In Decisions
Example 1: Blown-in chosen for a vented attic in Chicago, Illinois
A homeowner with R-11 existing batts in a 1,000 sq ft vented attic (Climate Zone 5). Got spray foam quote: $22,000 to R-49 equivalent with closed-cell. Got blown-in cellulose quote: $3,200 including air sealing. Chose blown-in cellulose. Installed: $3,200. Federal 25C credit on materials: $450. Net: $2,750. Annual savings: $380. Payback: 7.2 years. The spray foam contractor acknowledged in the quote meeting that closed-cell spray foam on a ventilated attic floor is not the cost-optimized choice and recommended blown-in himself for this application; the homeowner had specifically requested both quotes to compare.
Example 2: Spray foam chosen for an unvented conditioned attic in Houston, Texas
A homeowner building a home addition with HVAC equipment in the attic (ducts running through an unconditioned attic on a hot Houston day lose 20 to 30 percent of their capacity to heat gain). Chose unvented conditioned attic design. Closed-cell spray foam at 3.5 inches (R-22.75) applied to roof deck underside: 650 sq ft of roof deck at $4.50/sq ft = $2,925. Added blown-in cellulose on the attic floor between the new conditioned portion and the rest of the attic as a transition. The HVAC efficiency improvement from a conditioned attic paid back the spray foam premium in approximately 5 years at Houston electricity rates; the contractor’s Manual J calculation confirmed the HVAC unit could be sized 0.5 ton smaller because of the conditioned attic design.
Example 3: Hybrid approach in Denver, Colorado
A homeowner with recessed lights, a large attic hatch, and multiple HVAC penetrations in a difficult-to-air-seal 1,300 sq ft attic (Climate Zone 5). Hybrid approach: spray foam air sealing at all penetrations, light covers, and attic hatch ($1,100 open-cell spray foam for air seal only), followed by blown-in fiberglass to R-49 ($2,340). Total: $3,440. The spray foam step sealed all the complex geometry around the recessed lights and HVAC penetrations perfectly; filling those same penetrations with foam cans by hand would have required 8 to 10 hours and still left gaps. The blown-in fiberglass then added the bulk R-value at the lowest material cost. This hybrid approach combined the air sealing strength of foam with the cost efficiency of blown-in for the bulk R-value addition.
The insulation calculator gives you side-by-side costs for blown-in and spray foam for your attic size and R-value target.
Compare Insulation Options →Frequently Asked Questions About Spray Foam vs Blown-In
Is spray foam better than blown-in insulation?
Spray foam is better when you need an air barrier and insulation in one material (unvented roof deck, rim joists, foundation walls). Blown-in is better when you are adding R-value to a vented attic floor or filling existing wall cavities, where the cost per R-value is 3 to 5 times lower than spray foam. Neither is universally better; the correct choice depends on the application, location, and whether air sealing can be done separately before insulation installation.
What is the R-value of spray foam vs blown-in?
Closed-cell spray foam achieves R-6.0 to R-7.0 per inch, the highest R-value per inch of any common residential insulation material. Open-cell spray foam achieves R-3.5 to R-3.8 per inch. Blown-in cellulose achieves R-3.2 to R-3.8 per inch. Blown-in fiberglass achieves R-2.2 to R-2.7 per inch. The superior R-value per inch of closed-cell foam matters most in space-constrained locations (narrow rim joists, thin wall cavities) where more inches of material cannot physically fit.
Can I add blown-in insulation over spray foam?
Yes. The hybrid approach (spray foam for air sealing, blown-in for bulk R-value) is a common professional technique that combines the air sealing strength of foam with the cost efficiency of blown-in. The spray foam is applied first at all penetrations, gaps, and air leakage pathways; after it cures, blown-in material is added on top to reach the target R-value. This approach costs significantly less than reaching the target R-value with spray foam alone and performs nearly as well in air sealing because the critical leakage paths are foam-sealed before the blown-in layer is added.
Does spray foam insulation last forever?
Closed-cell spray foam does not degrade in normal building conditions; it maintains its R-value and air sealing performance indefinitely when protected from UV light (UV degrades the foam surface; it must be covered in exposed locations). Open-cell spray foam is vapor-permeable and can absorb moisture in very wet conditions; it is not appropriate for below-grade applications or in direct contact with the roof deck in climates where interior moisture condensation on the foam is possible without a vapor retarder. Properly applied in the correct application, spray foam is effectively permanent.
Can blown-in insulation get wet?
Cellulose blown-in absorbs moisture readily (borate treatment helps with pest resistance but not moisture absorption) and must dry before mold growth begins. Wet cellulose compresses and loses R-value during wetting; it recovers some R-value as it dries but may settle more than dry-installed cellulose after a wetting event. Blown-in fiberglass does not absorb moisture and retains its R-value when wet (water is not held by the glass fiber matrix), though it must be allowed to dry to prevent any associated structural moisture damage. Neither blown-in material should be used where chronic moisture exposure is expected; spray foam is the correct choice in those environments.
Is spray foam worth the extra cost in a home with old ductwork in the attic?
Yes, in many cases. Ductwork in a vented attic loses 20 to 30 percent of its capacity to the unconditioned attic environment in extreme weather. Moving ductwork inside the thermal envelope (by creating a conditioned attic with spray foam at the roof deck) improves HVAC efficiency dramatically. The spray foam cost at the roof deck is often offset by the ability to use a smaller, less expensive HVAC system than would be required with ducts in an unconditioned attic. If your HVAC equipment is located in the attic, have an energy auditor evaluate whether a conditioned attic design justifies spray foam at the roof deck for your specific home and climate.
What is open-cell vs closed-cell spray foam?
Open-cell spray foam has small cells that remain open (not fully closed), producing a soft, spongy material with R-value of 3.5 to 3.8 per inch. It is vapor-permeable, which allows walls to dry inward. Closed-cell spray foam has cells that are fully sealed during expansion, producing a rigid, dense material with R-value of 6.0 to 7.0 per inch. It is vapor-impermeable (Class II vapor retarder at 2 inches), which prevents moisture movement through the foam. Open-cell is less expensive ($1 to $2 per sq ft) and better for interior wall applications where vapor permeability is desirable. Closed-cell is more expensive ($3 to $7 per sq ft) and used for roof decks, rim joists, and any application requiring both insulation and a vapor retarder.
How long does spray foam insulation take to install?
Professional spray foam application takes 2 to 8 hours for a typical residential attic or crawl space application, depending on size and complexity. The foam must off-gas for 24 hours after application before the space is occupied; some foam formulations require 24 to 48 hours off-gas time with adequate ventilation. DIY spray foam kits (2-component canisters) are available for small air sealing applications (rim joists, penetrations) but are not practical for whole-attic applications; professional two-component proportioning equipment is required for large-scale spray foam insulation work.
Related Calculators and Guides
For insulation material specifications and fire safety ratings, the Spray Polyurethane Foam Alliance (SPFA) provides contractor training standards and product performance data. The DOE Types of Insulation guide covers R-values, applications, and performance data for all common residential insulation materials.