Blown-In Fiberglass vs Cellulose vs Spray Foam: Best Attic Insulation for Florida's Climate

Florida's climate is uniquely demanding on attic insulation. Summer sun bakes roof decks to 150°F, humidity saturates the air for six months, and AC units run ten months a year. A material that performs well in a dry climate can fail in Florida — settling, absorbing moisture, or trapping condensation that rots your roof deck.

This guide compares the three main attic insulation materials available to Florida homeowners — blown-in fiberglass, cellulose, and spray foam — on the factors that matter most for our climate: cost, R-value, lifespan, and moisture performance.

Quick Comparison

| Factor | Blown-In Fiberglass | Cellulose | Spray Foam | |---|---|---|---| | Cost (typical FL home) | $2,200–$7,800 | $2,000–$7,000 | $8,000–$20,000+ | | R-value per inch | R-2.2–R-2.5 | R-3.0–R-3.8 | R-3.7 (open) / R-6.5 (closed) | | Lifespan | 30+ years | 15–25 years | 20–30 years | | Settling | None | 20–30% over 5–10 years | Minimal | | Moisture resistance | Excellent (non-absorbent) | Poor (absorbs moisture) | Risk (can trap moisture) | | Payback period | 3–5 years | 4–6 years | 10–15 years |

Blown-In Fiberglass (Recommended for Florida)

Blown-in fiberglass is the material we install in every Florida attic, and for good reason. It's installed with a truck-mounted blowing machine that fills every gap, void, and irregularity — delivering uniform R-value across the entire attic floor with no thermal shortcuts.

Why Fiberglass Wins in Florida

No settling. Blown-in fiberglass retains its rated R-value for 30+ years without settling. Cellulose settles 20–30% over its first 5–10 years, meaning an R-38 cellulose install can drop to R-27 within a decade. In Florida, where cooling costs are significant, that performance loss directly costs you money every month.

Moisture resistance. Florida's humid summers expose attics to significant moisture. Fiberglass is naturally non-absorbent — it sheds water, retains its R-value when wet, and dries completely. Cellulose absorbs moisture, clumps, and can harbor mold — a serious problem in Florida's humidity. Spray foam can trap moisture against the roof deck, hiding damage until it's severe.

Fire resistance. Premium fiberglass is fire-resistant without chemical additives. Cellulose relies on chemical fire retardants that can leach out over time.

Cost-effectiveness. Fiberglass delivers proven R-value at a fraction of the cost of spray foam, with a payback period of 3–5 years vs 10–15 years for spray foam. The energy savings difference between the two is minimal — both cut cooling bills 15–30% — but fiberglass costs 3–5x less.

The One Limitation

Fiberglass doesn't air-seal on its own — it slows heat transfer but doesn't stop air movement through gaps. That's why every InsulX install includes air sealing as a standard step. Sealed + insulated performs dramatically better than insulated alone.

Cellulose

Cellulose is made from recycled paper, treated with fire retardants, and blown in with equipment similar to fiberglass. It's a common alternative and slightly cheaper per bag, but it has a critical weakness for Florida homes: it settles and absorbs moisture.

The Settling Problem

Cellulose settles 20–30% over its first 5–10 years as the fibers compact under their own weight. A Florida attic insulated with cellulose at R-38 today may perform at R-27 in a decade — and the performance loss continues as settling progresses. You pay for R-38 but get R-27 within 10 years.

Moisture Sensitivity

Cellulose absorbs moisture more readily than fiberglass, which is a serious concern during Florida's humid summers. Wet cellulose clumps, loses R-value, and can harbor mold — problems that require removal and replacement to fix.

When Cellulose Might Make Sense

Cellulose can be a reasonable choice for Florida homeowners on a very tight budget who plan to sell within 5 years — before significant settling occurs. But for anyone planning to stay in their Florida home longer than that, fiberglass is the better investment.

Spray Foam

Spray foam offers the highest R-value per inch of any insulation material and air-seals as it expands. It's an impressive product — but for Florida attics, the cost and moisture risks usually outweigh the benefits.

The Cost Problem

Closed-cell spray foam in a Florida attic runs $8,000–$20,000+ — 3–5x the cost of blown-in fiberglass to the same R-value. The energy savings difference between the two is minimal (both cut bills 15–30%), so the payback period for spray foam stretches to 10–15 years vs 3–5 years for fiberglass.

The Moisture Risk

In Florida's humid climate, spray foam applied to the underside of the roof deck can trap moisture against the sheathing if the building envelope isn't perfectly air-sealed. This can lead to roof deck rot — a costly problem that's nearly impossible to detect until it's severe. Blown-in fiberglass on the attic floor avoids this risk entirely.

When Spray Foam Makes Sense

Spray foam is best reserved for specific applications where its air-sealing and moisture properties add unique value — like rim joists, crawl spaces, or areas with unusual geometry. For standard Florida attics, blown-in fiberglass on the floor is the safer, more cost-effective choice.

The Verdict for Florida Homes

For 90% of Florida homes, blown-in fiberglass to R-38+ with air sealing is the right choice. It delivers:

• Proven R-value that lasts 30+ years without settling
• Excellent moisture resistance for Florida's humid summers
• The best cost-to-savings ratio of any material
• A 3–5 year payback (2–4 years with rebates and tax credits)
• No moisture risk to the roof deck

The exceptions are homes with specific needs (rim joists, crawl spaces) where spray foam's air-sealing adds unique value. For standard attic insulation across Florida, fiberglass is the clear winner.

Getting Started

Use our instant quote tool to get a projected cost range for your Florida home in under a minute — no callback required. Every quote is itemized and locked before installation begins, and every install includes air sealing, premium fiberglass to verified depth, and our 90-day performance guarantee.