Blown-In Fiberglass vs Spray Foam: Cost, Performance, and Climate Comparison

This is the most common question homeowners ask when researching attic insulation: blown-in fiberglass or spray foam? Spray foam is marketed as the premium, high-performance option, while blown-in fiberglass is positioned as the value choice. But the real comparison is more nuanced — and for most Florida and Indiana homeowners, the value choice is also the smarter choice.

Here's an honest, side-by-side comparison on the factors that actually matter: cost, R-value, air sealing, moisture performance, lifespan, and payback.

The Quick Comparison

| Factor | Blown-In Fiberglass | Spray Foam | |---|---|---| | Cost (typical home) | $2,200–$7,800 | $8,000–$20,000+ | | R-value per inch | R-2.2–R-2.5 | R-3.7 (open cell) / R-6.5 (closed cell) | | Air sealing | No (requires separate air sealing step) | Yes (expands to seal gaps) | | Lifespan | 30+ years | 20–30 years | | Moisture risk | None | Can trap moisture against roof deck | | Payback period | 3–5 years | 10–15 years |

Cost: The Biggest Difference

This is where the comparison gets stark. Spray foam costs 3–5x more than blown-in fiberglass for the same attic:

• Blown-in fiberglass: $2,200–$7,800 for a typical Florida or Indiana home
• Spray foam (closed cell): $8,000–$20,000+ for the same home

That's not a marginal difference — it's the difference between a project that pays for itself in 3–5 years and one that takes 10–15 years to pay back. For most homeowners, that payback gap is the deciding factor.

R-Value: Higher per Inch, But...

Spray foam's main advantage is R-value per inch — closed-cell spray foam delivers R-6.5 per inch vs fiberglass's R-2.5 per inch. That means spray foam achieves the same total R-value in less thickness.

But here's the catch: in an attic, you have the depth. Attic floors aren't thickness-constrained the way walls are. You have 10–20 inches of depth available, which is more than enough for blown-in fiberglass to reach R-38 to R-49 — the full R-value recommended for both Florida and Indiana. The higher per-inch R-value of spray foam is an advantage in walls, not attics.

Air Sealing: Spray Foam's Real Advantage

Spray foam's genuine advantage is that it air-seals as it expands — filling and sealing gaps in one step. Blown-in fiberglass doesn't air-seal on its own; it requires a separate air-sealing step before installation.

But here's the thing: that separate air-sealing step is standard and included in every professional blown-in install. When air sealing is done properly before blowing in fiberglass, the combined system delivers the same air-sealing benefit as spray foam — at a fraction of the cost.

The question isn't "does spray foam air-seal better?" — it's "is it worth paying 3–5x more for air sealing that's already included in a blown-in install?" For most homeowners, the answer is no.

Moisture Performance: Where Spray Foam Gets Risky

This is the comparison that's most often glossed over, and it matters enormously in both Florida and Indiana.

Blown-In Fiberglass: Moisture-Safe

Fiberglass is naturally non-absorbent. It sheds water, retains its R-value when wet, and dries completely. In Florida's humid summers and Indiana's freeze-thaw winters, this moisture tolerance is a significant advantage — there's no risk of trapped moisture causing hidden damage.

Spray Foam: Moisture Risk

Spray foam — especially when applied to the underside of the roof deck — can trap moisture against the sheathing if the building envelope isn't perfectly air-sealed. In Florida's humidity, this can lead to roof deck rot: a costly problem that's nearly impossible to detect until it's severe. In Indiana's freeze-thaw climate, trapped moisture can cause condensation that rots the deck over multiple seasons.

This isn't a theoretical risk — it's a documented problem in humid climates where spray foam is applied to roof decks. The fix (removing the foam and repairing the deck) can cost more than the original installation.

Lifespan and Durability

• Blown-in fiberglass: 30+ years with no settling or degradation
• Spray foam: 20–30 years; can shrink and pull away from framing over time, creating air gaps

Both last a long time, but fiberglass has the edge in longevity and doesn't develop the shrinkage gaps that spray foam can over decades.

When Spray Foam Actually Makes Sense

Spray foam isn't wrong for every application — it's the right choice for specific situations:

• Rim joists and crawl spaces — enclosed spaces where its air-sealing and moisture properties add unique value
• Walls with limited cavity depth — where high R-value per inch matters
• Homes with unusual geometry — where blown-in can't reach effectively

For standard attic floor insulation in Florida and Indiana, though, blown-in fiberglass on the floor is the safer, more cost-effective choice.

The Verdict

For attic insulation in Florida and Indiana, blown-in fiberglass with professional air sealing is the better choice for 90% of homes. It delivers:

• The same energy savings (15–30% bill reduction) as spray foam
• The same air-sealing benefit (when air sealing is included, as it should be)
• No moisture risk to the roof deck
• A 3–5 year payback vs 10–15 years for spray foam
• 30+ year lifespan with no shrinkage

You get the performance without paying 3–5x more, and without the moisture risk. For most homeowners, that's the definition of a smart investment.

Getting Started

Every InsulX attic install uses blown-in fiberglass with included air sealing — delivering spray-foam-level performance at a fraction of the cost, with no moisture risk. Use our instant quote tool to get a projected cost range for your Florida or Indiana home in under a minute.