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Spray Foam vs Fiberglass vs Blown-In: Which Is Best for Florida Homes?
Ideal Insulation
Every Florida homeowner shopping for insulation hits the same fork: spray foam costs more upfront, fiberglass is cheap, and blown-in is in the middle. Which one actually makes sense when you live in a state where humidity tries to destroy everything?
We've installed all three across thousands of Southwest Florida homes since 2013. Here's the honest comparison.
The Quick Comparison
| Factor | Closed Cell Spray Foam | Open Cell Spray Foam | Blown-In Fiberglass | Fiberglass Batts |
|---|---|---|---|---|
| R-Value Per Inch | R-6.5 | R-3.7 | R-2.5 | R-3.1 |
| Air Sealing | Yes | Yes | No | No |
| Moisture Barrier | Yes | No | No | No |
| Cost Per Sq Ft | $2-4 | $1-2 | $0.50-1.25 | $0.30-1.00 |
| Lifespan | 20+ years | 20+ years | 10-15 years | 10-15 years |
| Mold Resistance | Excellent | Good | Poor | Poor |
| Hurricane Resistance | Adds structural strength | Minimal | None | None |
Why This Comparison Is Different in Florida
1. Humidity Is the Enemy
Southwest Florida averages 74% relative humidity. In summer, it's 85-95%. When warm, humid air hits a cool surface (your air-conditioned ceiling), condensation forms. Inside fiberglass insulation, that means mold growth, R-value collapse, and structural damage over time.
Spray foam — especially closed cell — doesn't absorb moisture. It seals the building envelope so humid air can't reach cool surfaces.
2. Your Attic Is an Oven
In July, a Naples attic hits 150-160°F. Your ductwork is up there, pumping 55°F air through ducts surrounded by 155°F air. Blown-in fiberglass on the attic floor tries to block heat but your ducts still cook.
Spray foam on the roof deck creates a conditioned attic. Temperature drops from 155°F to 85-90°F. Ducts stay cool. AC runs less. Bill drops 30-40%.
3. Hurricane Season Is Real
After Hurricane Ian in 2022, homes with closed cell spray foam on the roof deck had significantly less structural damage. It bonds sheathing to trusses, increasing wind uplift resistance by up to 300%.
When Each Type Makes Sense
Closed Cell Spray Foam — The Premium Choice
Best for: Crawl spaces, coastal homes, flood zones, garages, exterior walls. At R-6.5 per inch with a moisture barrier, it's the gold standard when moisture is the primary concern.
Open Cell Spray Foam — The Smart Middle Ground
Best for: Attic roof decks, interior walls, soundproofing, most residential applications. Excellent air seal at half the cost of closed cell. This is what we install in the majority of Naples attics.
Blown-In Fiberglass — The Budget Option
Best for: Supplementing existing insulation, flat attic floors on a tight budget, rental properties. Quick and cheap but doesn't air seal, settles 20-30% over time, and holds moisture.
Fiberglass Batts — Economy Choice
Best for: Interior partition walls for soundproofing. Not recommended as primary insulation in Florida's exterior envelope — gaps at every stud, wire, and pipe let humid air through.
10-Year Cost vs. Value (1,500 sq ft attic)
| Blown-In | Open Cell Foam | Closed Cell Foam | |
|---|---|---|---|
| Install cost | $1,125 | $2,250 | $4,500 |
| FPL rebate | -$220 | -$220 | -$220 |
| Net cost | $280 | $1,405 | $3,655 |
| Annual savings | $600 | $1,100 | $1,200 |
| 10-year savings | $6,000 | $11,000 | $12,000 |
| 10-year net return | $5,720 | $9,595 | $8,345 |
| Needs replacement? | Yes (10-15 yrs) | No | No |
Open cell delivers the highest 10-year ROI for most Naples homeowners.
Our Recommendation for Most SWFL Homes
- Attic: Open cell spray foam on the roof deck
- Crawl spaces: Closed cell spray foam
- Exterior walls (new construction): Open cell in cavities
- Interior walls: Fiberglass batts for sound dampening
- Coastal/flood zone: Closed cell throughout
Still Not Sure?
Our free thermal leak scan shows exactly where energy escapes and which insulation makes the most impact for your specific home.
