Spray Foam Insulation
Core spray foam pages that explain material types, costs, R-values, and common alternatives.
Spray Foam vs Blown-In Insulation: Which Wins?
Two popular attic options, two very different jobs — compared for homes across Hamilton County. Here's how cost, R-value, and air-sealing really stack up.
Quick Answer
Blown-in cellulose is cheaper (about $0.60 to $2.30 per square foot installed) and great for covering an open attic floor to R-49. Spray foam costs more but air-seals — which blown-in doesn't — and works on rooflines and walls cellulose can't. For a vented attic floor, blown-in wins on price; for a sealed attic, air-leakage problems, or a finished roofline, spray foam wins on performance.
Spray Foam vs Blown-In Cellulose
| Feature | Spray Foam | Blown-In Cellulose |
|---|---|---|
| Air Seal | Yes — seals gaps and penetrations | No (partial if dense-packed) |
| R-Value per Inch | R-3.6 (open-cell) to R-6.5 (closed-cell) | R-3.2 to R-3.8 |
| Installed Cost | Higher | Lower ($0.60 - $2.30 per sq ft) |
| Best Location | Rooflines, walls, sealed attics | Open, vented attic floors |
| Moisture Barrier | Closed-cell only | No |
| Settling Over Time | None | Settles 10% to 20%, reducing R-value |
Air Seal
Spray Foam
Yes — seals gaps and penetrations
Blown-In Cellulose
No (partial if dense-packed)
R-Value per Inch
Spray Foam
R-3.6 (open-cell) to R-6.5 (closed-cell)
Blown-In Cellulose
R-3.2 to R-3.8
Installed Cost
Spray Foam
Higher
Blown-In Cellulose
Lower ($0.60 - $2.30 per sq ft)
Best Location
Spray Foam
Rooflines, walls, sealed attics
Blown-In Cellulose
Open, vented attic floors
Moisture Barrier
Spray Foam
Closed-cell only
Blown-In Cellulose
No
Settling Over Time
Spray Foam
None
Blown-In Cellulose
Settles 10% to 20%, reducing R-value
Each Option's Trade-Offs
Spray Foam
Pros
- Air-seals and insulates in one step
- Higher R-value per inch, so it fits thinner spaces and rooflines
- Doesn't settle or lose R-value over time
- Closed-cell adds a moisture barrier where needed
Cons
- Higher upfront cost than blown-in
- Requires professional installation
Blown-In Cellulose
Pros
- Lowest cost to bury an open attic floor in R-49
- Fast to install over a large, accessible attic floor
- Made largely from recycled paper
Cons
- No air sealing — leaks pass right through it
- Settles 10% to 20% over time, lowering effective R-value
- Can't insulate a roofline, knee wall, or finished ceiling
- Loses performance if it gets wet
The Cost Reality
A blown-in cellulose attic typically runs about $3,000 to $7,000, with a national average near $5,000. Open-cell spray foam at the roofline costs more, but it does a different job — it air-seals the attic and converts it to conditioned space. So the comparison isn't just cheaper versus pricier; it's two different outcomes. Blown-in buries the attic floor in insulation; spray foam seals the envelope at the roof. Which one is right depends on your attic, not just your budget.
Which for an Indiana Attic?
For a standard vented attic with an open, accessible floor and no ductwork up there, blown-in cellulose to R-49 is the most cost-effective choice — Indiana's energy code calls for R-49 in the attic. But if the attic is sealed or conditioned, the ceiling is vaulted, ductwork runs through the attic, or the home has chronic air-leakage problems, open-cell spray foam at the roofline is the better performer. The EPA estimates sealing and insulating cuts heating and cooling costs by about 15% on average, and that air seal is exactly what blown-in can't provide.
Our Verdict
Spray foam and blown-in aren't really competitors — they solve different problems. Blown-in cellulose is the cost-effective way to bury an open attic floor in R-49. Spray foam is what you use when you need an air seal or you're insulating the roofline itself. We'll tell you which your attic actually needs on a free quote. For attic-specific guidance, see our Best Insulation for Attics guide.
Frequently Asked Questions
It depends on the attic. For an open, vented attic floor, blown-in cellulose to R-49 is more cost-effective. For a sealed attic, a finished roofline, or a home with serious air leakage, spray foam is better because it air-seals — something blown-in can't do.
Not directly. Spray foam needs to bond to a clean substrate like the roof deck or framing, so loose blown-in material in the path of a roofline application should be removed first. If you're insulating the attic floor instead, adding more blown-in on top of existing blown-in is straightforward.
Spray foam lasts the life of the building without settling or losing R-value. Blown-in cellulose settles 10% to 20% over time, which lowers its effective R-value and may eventually call for a top-up. That durability is part of spray foam's long-term value.
Spray foam's air seal usually gives it the edge. The EPA estimates that sealing air leaks and adding insulation cuts heating and cooling costs by about 15% on average, and blown-in alone doesn't stop air movement. On an open attic floor with good existing air sealing, though, blown-in to R-49 performs well for far less money.
Related
Related resources
Attic Insulation
Attic-focused pages for roof decks, air sealing, foam type selection, and cost planning.
Related Services
Open-Cell Foam
Cost-effective spray foam for attics and interior assemblies where comfort and sound control matter.
- Lowest cost per board foot of any spray foam
- Noticeably quieter, reduces sound between rooms and from outside
- Great for attics, interior walls, and bonus rooms
Closed-Cell Foam
High R-value insulation with moisture resistance for crawl spaces, basements, metal buildings, and demanding envelopes.
- Highest R-value of any spray-applied insulation (R-6.5 per inch)
- Acts as a vapor barrier
- Won't absorb water — ideal for moisture-prone areas
Attic Insulation
Stop losing heat through the roof. We insulate attics for year-round comfort and lower energy bills.
- Reduce heating and cooling costs immediately
- Prevent ice dams in winter
- Create usable conditioned attic space
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