Spray Foam vs. Blown-In Insulation: Which Is Worth It?
Which one to pick
Blown-in is the budget winner for open attics — it fills a big space fast and cheap, and the R-value per dollar is hard to beat. Spray foam costs more but does more: it air-seals as it insulates, hits a higher R-value in less depth, and shines in rim joists, crawlspaces, and walls where stopping air leaks matters most. The smart play in many homes is both — blown-in across the attic floor, spray foam to seal the trouble spots.
Adding insulation usually means choosing between spray foam and blown-in — the premium air-sealer versus the budget cavity-filler. Both lower your energy bills; they just do it differently, and in different parts of the house.
Blown-in loose-fill (cellulose or fiberglass) is blown into attics and open cavities, cheap and fast. Spray foam expands to seal every gap and packs a much higher R-value per inch, at a higher price. Here’s where each one earns its keep.
| Factor | Spray foam | Blown-in |
|---|---|---|
| Installed cost | $1.50 – $4.50 / sq ft | $1 – $2.50 / sq ft |
| R-value per inch | R-6 to R-7 (closed-cell) | R-2.2 to R-3.8 |
| Air sealing | Excellent — seals gaps itself | Modest — fills, doesn't fully seal |
| Moisture / vapor | Closed-cell blocks moisture | Doesn't stop air or vapor |
| Best place | Rim joists, crawlspaces, walls, roof deck | Attics, large open cavities |
| DIY? | No — professional install | Possible for attics (rental blower) |
| Best for | Max efficiency, air sealing, tight spaces | Big areas on a budget |
Common questions
- Is spray foam worth the extra cost over blown-in?
- In spots where air leakage drives bills — rim joists, crawlspaces, knee walls — yes. Spray foam seals and insulates in one step. For a big open attic, blown-in delivers more R-value per dollar, so foam's premium is harder to justify there.
- Which has the higher R-value?
- Spray foam. Closed-cell foam is R-6 to R-7 per inch versus R-2.2 to R-3.8 for blown-in, so foam reaches the same R-value in roughly half the thickness — useful where space is tight.
- Which is cheaper?
- Blown-in, at $1–$2.50 per square foot versus $1.50–$4.50 for spray foam. For a typical attic, blown-in can cost half as much as foam.
- Can I install either myself?
- Blown-in is DIY-friendly for attics with a rented blower. Spray foam should be left to pros — mixing, ratios, and curing are easy to get wrong, and bad foam is expensive to remove.
How we estimate: We checked these prices against the 2026 sources listed below (see how we get our numbers). Your price depends on where you live, so get two or three written bids.
Sources
We checked the prices on this page against 2026 numbers from these sources:
- Spray Foam Insulation Cost (2026), HomeGuide
- Blown-In Insulation Cost (2026), HomeGuide
- Types of Insulation, U.S. Department of Energy