Blown-In vs. Batt Insulation
Blown-in insulation costs $1.50 to $3.00 per square foot installed; fiberglass batts cost $1.00 to $2.50 per square foot installed. For most existing attics, blown-in wins on performance because it fills around obstacles; batts win on price in clear, uniform spaces. But the honest headline: the choice between them matters less than air sealing first and installation quality throughout. This guide compares costs, R-values, and use cases — no product endorsements, just the tradeoffs.
Orange County, CA · Updated 2026 · Costs shown as ranges — your quote will vary by contractor and scope
Cost head-to-head, installed
Blown cellulose: $1.50 to $2.50/sq ft installed. Blown fiberglass: $1.80 to $3.00. Fiberglass batts: $1.00 to $2.50 installed ($0.50 to $1.50 materials-only). For 1,000 sq ft: roughly $1,500–$3,000 blown-in versus $1,000–$2,500 batts. Removal, where needed, adds $1.00 to $2.00/sq ft either way.
Depth is where cheap quotes cheat: R-38 needs ~12 inches of fiberglass or 10 of cellulose. A quote without target depth and R-value isn't comparable to one with it. Demand both in writing; depth rulers left in the attic are the proof.
DIY math: batts in a clear attic (straightforward if tedious), blown top-ups over existing insulation (one long day, P100 respirator required). What DIY can't replicate cheaply: the pro air-sealing pass ($500 to $1,200) that should precede either material.
R-values and what they actually mean
Blown cellulose: R-3.2 to R-3.8/inch. Blown fiberglass: R-2.5 to R-3.7/inch. Batts: R-3.0 to R-3.7/inch at full loft — the catch: a batt compressed from its labeled thickness performs well below its rating. Compression is the silent R-value killer.
Cellulose settles 10 to 20% in the first years — pros blow 15 to 20% deep to compensate (the quote should state settled vs. installed depth). Fiberglass settles less but shifts in windy attics. What degrades isn't R-value but coverage: wind washing, critter tunneling, storage compression.
R-38 is the practical mild-climate target (~12 inches blown fiberglass). Past R-38, each added R buys less — in coastal California, R-49 over R-38 pays back in decades. Spend the marginal dollar on air sealing.
Where each one wins
Blown-in wins: existing attics with pipes, wires, ducts, and can lights (nearly all of them); topping up; irregular joist spacing. It flows around obstacles that defeat batts, and crews blow 1,000 sq ft in hours.
Batts win: new construction and gutted attics with clear, uniform bays; floors and walls at standard framing; tight budgets with genuinely clear space. Also the no-special-equipment DIY pick — batts, a utility knife, patience.
The pro-recommended hybrid: air seal everything, then blow over the top. Remodel walls: dense-pack cellulose ($2.00 to $3.50/sq ft of wall) beats batts around wiring and plumbing. Floors over garages/crawlspaces: supported batts (wire stays, no sagging), encapsulated where moisture threatens.
The thing that matters more: air sealing
Insulation slows heat transfer; it does nearly nothing about air moving through gaps — and attics are full of them: top plates, penetrations, recessed lights, hatches, chases. Blown insulation over unsealed penetrations is home performance's most common half-job.
Air sealing ($500 to $1,200: caulk, foam, mastic at every penetration, weatherstripped hatch) routinely beats insulation on comfort-per-dollar, especially in older homes. Attic leaks drive whole-house infiltration via the stack effect — the top of the envelope is the highest-leverage seal point.
Buy it right: get insulation-only and insulation+air-sealing quotes from each bidder — the delta should be $500 to $1,200, not $3,000. Get the sealing scope in writing. Verify with depth rulers and a look for foam rings and caulked plates; a post-job infrared scan ($150 to $300) is gold-standard proof.
Blown-in vs. batt insulation comparison (2026)
| Factor | Blown-in |
|---|---|
| Installed cost / sq ft | $1.50 – $3.00 |
| Materials-only / sq ft | $0.60 – $1.20 |
| R-value per inch | R-2.5 – R-3.8 |
| Best for | Existing attics, topping up, obstacles |
| Settling | 10–20% (cellulose); blow deep |
| DIY difficulty | Moderate (blower + respirator) |
| Air sealing still needed | Yes — always |
DIY vs. hiring a pro
DIY decision tree: clear attic + batts = very DIYable; top-up = DIYable with blower loan and P100 respirator; air sealing in tight attics, vermiculite, or spray foam = hire out. The classic DIY error: insulating over unsealed penetrations — air-seal first ($30 of caulk and foam, one weekend). Depth targets: 12 in fiberglass / 10 in cellulose for R-38. Never cover soffit vents — $1 baffles keep the channel open; skipped baffles are the most common DIY moisture mistake.
What drives the price up or down
- Attic condition — obstacles favor blown-in; clear bays favor batts
- Depth honesty — quotes must state inches and R-value
- Air sealing — the upgrade that outranks the material choice
- Settling & compression — blow deep; don't compress batts
- DIY vs. pro — equipment and misery vs. labor cost
- Verification — depth rulers and post-job inspection
How to keep the cost down
- Always price insulation + air sealing together, not insulation alone
- Demand target depth and R-value in writing from every bidder
- For topping up, blown-in beats batts in nearly every real attic
- Don't pay for R-49 in mild climates — diminishing returns
- Keep soffit vents clear with baffles ($1 each)
- Verify with depth rulers left in the attic
Frequently asked questions
Is blown-in insulation better than batts?
For most existing attics, yes: blown-in fills around obstacles and forms a uniform blanket. Batts are cheaper and fine in clear bays — but compressed or gapped batts underperform badly.
How much does blown-in insulation cost per square foot?
$1.50 to $3.00 installed ($1.50–$2.50 cellulose, $1.80–$3.00 fiberglass). A 1,000 sq ft top-up to R-38 runs roughly $1,500–$3,000 before air sealing.
What R-value should attic insulation be?
R-38 (about 12 inches of blown fiberglass or 10 of cellulose). Beyond R-38, returns diminish fast; spend the difference on air sealing.
Does insulation need air sealing first?
Yes. Insulation doesn't stop air leakage, and attics leak at every penetration. Air sealing ($500–$1,200) plus insulation is the combination that performs.
Can I install blown-in insulation myself?
Yes for top-ups: free blower loans with bulk purchases, one long day. Wear a P100 respirator, air-seal first, don't cover soffit vents, hit target depth (12 in fiberglass / 10 in cellulose).