Spray Foam vs Blown-In Insulation: Cost & Performance Comparison

Spray Foam vs Blown-In Insulation: Which One Is Right for Your Home?

If you're insulating your home — whether it's a new build, a renovation, or just trying to stop that cold draft from turning your living room into a walk-in freezer — you've probably narrowed your options down to two popular choices: spray foam insulation and blown-in insulation. Both are excellent options, but they work differently, cost differently, and perform differently depending on where you use them.

In this guide, we'll compare spray foam and blown-in insulation on every metric that matters: R-value per inch, cost, moisture resistance, air sealing, installation difficulty, and ideal applications. By the end, you'll know exactly which type of insulation makes sense for each part of your home.

Understanding the Two Options

Spray Foam Insulation

Spray foam is a liquid polyurethane that expands dramatically when applied, filling every crack, gap, and cavity it touches. It comes in two varieties:

• Open-cell spray foam: Softer, less dense, lower R-value, but more affordable. Good for interior walls and sound dampening.
• Closed-cell spray foam: Dense, rigid, high R-value, acts as a vapor barrier. Premium option for exterior walls, basements, and crawl spaces.

Blown-In Insulation

Blown-in insulation consists of loose-fill material that's mechanically blown into cavities using a special machine. The two most common materials are:

• Cellulose: Made from recycled paper treated with fire retardant. Good R-value, eco-friendly, affordable.
• Fiberglass: Made from tiny glass fibers. Doesn't absorb moisture, won't settle as much over time.

Head-to-Head Comparison

Factor	Spray Foam (Closed-Cell)	Spray Foam (Open-Cell)	Blown-In Cellulose	Blown-In Fiberglass
R-Value per Inch	R-6.0 to R-7.0	R-3.5 to R-3.8	R-3.2 to R-3.8	R-2.2 to R-2.7
Cost per Sq Ft	$1.50–$3.50	$0.75–$1.50	$0.60–$1.20	$0.50–$1.00
Air Sealing	Excellent	Good	Moderate	Poor
Moisture Barrier	Yes (built-in)	No	No	No
Sound Dampening	Good	Excellent	Very Good	Good
Settling Over Time	None	None	10–20% settling	Minimal
DIY Feasible	No	No	Yes (rental equipment)	Yes (rental equipment)
Eco-Friendly	Low	Moderate	High (recycled)	Moderate
Lifespan	80+ years	80+ years	20–30 years	30–40 years

R-Value: The Performance Metric

R-value measures thermal resistance — the higher the number, the better the insulation prevents heat transfer. Here's why this matters in practice:

To achieve R-38 (the recommended attic insulation level for most US climate zones), you'd need:

• Closed-cell spray foam: About 5.5 inches
• Open-cell spray foam: About 10 inches
• Blown-in cellulose: About 10.5 inches
• Blown-in fiberglass: About 15 inches

This is why closed-cell spray foam is popular in tight spaces like rim joists or thin wall cavities — you get more thermal protection in less space. But if you're insulating a wide-open attic with plenty of room, blown-in is far more cost-effective for the same R-value.

Cost Comparison: The Full Picture

Let's price out a typical insulation project — a 1,500 sq ft attic:

Insulation Type	Material + Labor	Total for 1,500 sq ft
Closed-cell spray foam (R-38)	$2.50–$3.50/sq ft	$3,750–$5,250
Open-cell spray foam (R-38)	$1.25–$2.00/sq ft	$1,875–$3,000
Blown-in cellulose (R-38)	$0.80–$1.20/sq ft	$1,200–$1,800
Blown-in fiberglass (R-38)	$0.70–$1.00/sq ft	$1,050–$1,500

Closed-cell spray foam costs roughly 3-4x more than blown-in for the same R-value. That premium buys you air sealing, moisture resistance, and an extremely long lifespan — but whether it's worth it depends on where you're insulating.

For a comprehensive breakdown of insulation costs in your area, check out our insulation cost guide.

Air Sealing: Where Spray Foam Dominates

This is spray foam's killer feature. When it expands, it fills every tiny gap, crack, and hole in the building envelope. Air leaks are responsible for 25-40% of heating and cooling energy loss in a typical home, and spray foam addresses this problem better than any other insulation type.

Blown-in insulation doesn't seal air leaks. It slows heat transfer through the insulation itself, but air can still move through and around it. If you choose blown-in, you should separately air-seal all penetrations (electrical boxes, plumbing pipes, recessed lights, etc.) with caulk and foam before blowing in the insulation.

Wondering how much you could save on energy bills? Try our energy savings calculator to estimate the impact of better insulation.

Moisture and Mold Considerations

Closed-cell spray foam is a vapor barrier. It doesn't absorb water, and it prevents moisture from passing through it. This makes it ideal for:

• Basement walls and rim joists
• Crawl spaces
• Exterior wall cavities in humid climates
• Areas prone to flooding or moisture intrusion

Blown-in cellulose can absorb moisture, which is both a pro and a con. The borate treatment provides some mold resistance, but if cellulose gets consistently wet (from a roof leak, for example), it can clump, settle, and lose effectiveness. Blown-in fiberglass doesn't absorb water but can trap moisture if not properly ventilated.

In humid climates like the Southeast US, this moisture consideration often tips the decision toward spray foam for certain applications.

DIY Feasibility

Here's a practical consideration that matters to a lot of homeowners:

Blown-in insulation: Very DIY-friendly. You can rent a blowing machine from most home improvement stores (often free with insulation purchase), and the process is straightforward — fill the hopper, point the hose, blow it in. A handy homeowner can insulate an attic in a weekend.

Spray foam insulation: Not a DIY project. Professional spray foam requires specialized equipment (a spray rig costing $20,000+), protective gear, and training. The chemicals are hazardous, and improper mixing ratios can create insulation that off-gasses indefinitely. Small DIY spray foam kits exist for filling gaps and cracks, but they're not practical for insulating an entire space.

Best Applications for Each Type

Use Closed-Cell Spray Foam For:

• Rim joists and band joists — The #1 recommended use. These areas need both insulation and air sealing
• Basement walls — Moisture resistance is critical underground
• Crawl spaces — Prevents moisture and air intrusion from below
• Cathedral ceilings — Where space is limited and you can't ventilate
• Exterior walls in renovations — When you can access wall cavities

Use Open-Cell Spray Foam For:

• Interior walls — Excellent soundproofing between rooms
• Attic roofline — Creating an unvented conditioned attic
• Above-grade walls — Where moisture isn't a primary concern

Use Blown-In Cellulose For:

• Attic floors — Most cost-effective option for open attic spaces
• Existing wall cavities — Can be dense-packed through small holes without removing drywall
• Budget-conscious projects — Best bang for your buck

Use Blown-In Fiberglass For:

• Attic floors — Slightly less settling than cellulose
• Areas where moisture is a concern — Doesn't absorb water like cellulose
• Budget projects — Lowest cost option

Energy Savings Comparison

The Department of Energy estimates that properly insulating your home can save 10-50% on heating and cooling costs, depending on your current insulation level and climate zone. Here's how the two compare in terms of real-world energy savings:

• Spray foam typically delivers 30-50% energy savings due to both insulation and air sealing
• Blown-in typically delivers 15-25% energy savings (higher if you also air-seal separately)

The gap narrows significantly if you do a thorough air-sealing job before blowing in insulation. The combination of air sealing + blown-in can approach spray foam's performance at a fraction of the cost.

Environmental Considerations

If you care about the environmental impact of your insulation choice:

• Cellulose is the clear winner — made from 75-85% recycled newspaper
• Fiberglass contains 40-60% recycled glass content
• Open-cell spray foam — some brands use water-blown formulations with lower environmental impact
• Closed-cell spray foam — uses chemical blowing agents with higher global warming potential, though newer HFO-blown formulations are much improved

Pros and Cons Summary

Spray Foam Pros

• Highest R-value per inch (closed-cell)
• Excellent air sealing — fills every gap
• Built-in vapor barrier (closed-cell)
• Doesn't settle or degrade over time
• 80+ year lifespan

Spray Foam Cons

• 3-4x more expensive than blown-in
• Must be professionally installed
• Difficult to remove or modify later
• Some formulations have higher environmental impact
• Off-gassing risk if improperly installed

Blown-In Pros

• Very affordable — best value per R-value dollar
• DIY-friendly with rental equipment
• Eco-friendly (especially cellulose)
• Easy to add more later if needed
• Works well in existing homes without major renovation

Blown-In Cons

• Doesn't seal air leaks
• Cellulose can settle 10-20% over time
• No moisture barrier
• Lower R-value per inch requires more thickness
• Shorter lifespan (20-40 years)

The Bottom Line

For most homeowners, the smartest approach is a combination strategy: use spray foam where it matters most (rim joists, basement walls, crawl spaces) and blown-in cellulose or fiberglass everywhere else (attic floors, wall cavities). This gives you the best performance where air sealing and moisture resistance are critical, without blowing your entire budget on spray foam in areas where blown-in works just fine.

If budget is your primary concern, blown-in cellulose with separate air sealing gives you 80-90% of spray foam's performance at 30-40% of the cost. That's a deal that's hard to beat.

Whatever you choose, properly insulating your home is one of the best investments you can make. Check our insulation cost guide for pricing in your area, and use our energy savings calculator to see how much you could save on utility bills.