Spray Foam vs Blown-In Insulation: Which Wins?

Two popular attic options, two very different jobs — compared for homes and metal-roofed buildings around Kokomo. 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

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.

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