Fiberglass vs. Cellulose Blown-In Insulation: Which Is Better for Florida?
Fiberglass and cellulose are both excellent blown-in insulation materials. Here is how they compare for South Florida attics — and which one Cardinal Insulation recommends.
When homeowners in Boca Raton, Delray Beach, and across Palm Beach County ask about blown-in insulation, one of the first questions is: "Should I use fiberglass or cellulose?" Both are excellent materials. But South Florida's specific climate conditions make one a better fit for most homes in our area.
Here's an honest comparison.
The Basics: What Each Material Is
Fiberglass blown-in insulation is made from spun glass fibers — the same material as traditional batt insulation, but processed into loose, fluffy form for blowing. It's inorganic, meaning it won't rot, mold, or decompose.
Cellulose blown-in insulation is made from recycled paper (typically 75–85% post-consumer content) treated with borate compounds for fire and pest resistance. It's one of the most environmentally friendly insulation options available.
R-Value Comparison
R-value measures thermal resistance per inch of material.
| Material | R-Value Per Inch | Inches Needed for R-38 | Inches Needed for R-60 |
|---|---|---|---|
| Fiberglass blown-in | 2.2–2.7 | 14–17 inches | 22–27 inches |
| Cellulose blown-in | 3.2–3.8 | 10–12 inches | 16–19 inches |
Cellulose achieves the same R-value in less depth. This matters in attics with limited headroom or where you want to maximize R-value without adding excessive weight.
Moisture Resistance: Critical in South Florida
This is where the comparison gets important for Palm Beach County homeowners.
Fiberglass: Inorganic and inherently moisture-resistant. It does not absorb water, does not support mold growth, and dries out without losing R-value after minor moisture exposure.
Cellulose: Made from paper, which is organic and hygroscopic (absorbs moisture). While borate treatments provide some protection, cellulose can absorb and retain moisture in humid conditions. In South Florida's subtropical climate — with average relative humidity above 70% year-round — this is a meaningful concern.
If your attic has any history of roof leaks, condensation issues, or inadequate ventilation, fiberglass is the safer choice.
Air Sealing Performance
Both materials provide good air sealing when properly installed. However, there are differences:
Cellulose has a slight edge in natural air sealing due to its denser packing. The material settles into gaps and crevices more completely.
Fiberglass is lighter and may leave small gaps around irregular penetrations if not installed carefully.
The good news: professional installation with proper pre-work (sealing penetrations before blowing) eliminates most of this difference. Cardinal Insulation seals all penetration points before installing either material.
Pest and Mold Resistance
Fiberglass: Naturally resistant to mold, insects, and rodents. There's nothing organic for pests to eat or mold to grow on.
Cellulose: Treated with borate compounds that provide fire resistance and some pest deterrence. However, borate treatments can leach out over time, particularly in humid conditions. Cellulose that has been wet may lose some of its pest-resistance properties.
In South Florida, where rodent activity in attics is common, fiberglass has a practical advantage.
Environmental Impact
Cellulose wins on environmental credentials. It's made from 75–85% recycled content, requires less energy to manufacture than fiberglass, and has a lower embodied carbon footprint.
Fiberglass is made from silica sand and recycled glass. Modern fiberglass products contain 20–30% recycled content — less than cellulose, but still a meaningful percentage.
If environmental impact is a priority for you, cellulose is the greener choice.
Cost Comparison
Material costs are similar, with cellulose typically running 10–15% less expensive per bag. However, because cellulose achieves higher R-value per inch, you may need fewer bags to reach your target R-value.
In practice, the total installed cost difference between fiberglass and cellulose blown-in is usually less than 10% for a typical South Florida attic.
What Cardinal Insulation Recommends for South Florida
For most homes in Boca Raton, Delray Beach, Boynton Beach, West Palm Beach, and Palm Beach Gardens, we recommend premium fiberglass blown-in insulation for the following reasons:
- Moisture resistance is critical in our subtropical climate
- Pest resistance matters in a region with active rodent populations
- Long-term performance — fiberglass maintains R-value without degradation from humidity
- No organic material means no mold risk even in the event of minor roof leaks
We do install cellulose when customers specifically request it or when project conditions favor it. Both materials are excellent when properly installed.
The Bottom Line
For South Florida attics, fiberglass blown-in insulation is the more durable long-term choice. Cellulose is a viable option and has environmental advantages, but the moisture and pest considerations in our climate tip the balance toward fiberglass for most homes.
The most important factor isn't which material you choose — it's the quality of the installation. Proper air sealing, correct depth, and adequate ventilation matter more than the material itself.
Cardinal Insulation serves all of Palm Beach County. Call (561) 654-7698 for a free attic assessment and material recommendation specific to your home.
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