Spray Foam vs. Blown-In Insulation: Which Is Worth It?
The verdict
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 |
Frequently asked 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: ranges are cross-checked against current 2026 industry sources (see our data & methodology). Your actual cost depends on local rates — always get multiple written quotes.
Sources
Cost ranges on this page were checked against current (2026) data from these industry sources:
- Spray Foam Insulation Cost (2026) — HomeGuide
- Blown-In Insulation Cost (2026) — HomeGuide
- Types of Insulation — U.S. Department of Energy