Blown-in insulation is one of the most cost-effective ways to improve a home’s energy efficiency, and the two materials owners compare most often are cellulose and fiberglass. Cellulose is made from recycled paper treated with borate for fire and pest resistance, while fiberglass is made from fine spun glass fibers. The right choice between cellulose vs fiberglass blown-in insulation depends on your climate, your attic or wall structure, and what you’re prioritizing: thermal performance, moisture resistance, sound control, or long-term cost.
Homes along the Gulf Coast deal with high humidity for much of the year, which makes this comparison especially important. Prestige Insulation Solutions has installed both blown-in insulation and fiberglass insulation across residential and commercial properties throughout Northwest Florida, and the breakdown below reflects that field experience alongside published performance data.
Cellulose vs Fiberglass Blown-In Insulation: Key Differences at a Glance
| Feature | Cellulose Blown-In | Fiberglass Blown-In |
|---|---|---|
| Material Composition | Recycled newspaper treated with borate | Spun glass fibers |
| R-Value per Inch | 3.2 – 3.8 | 2.2 – 2.7 |
| Moisture Sensitivity | Higher (can absorb moisture) | Lower (resists moisture) |
| Fire Resistance | High (treated with fire retardants) | High (naturally non-combustible) |
| Settling Over Time | Yes, around 20% in the first year | Minimal |
| Air Sealing Capability | Excellent | Moderate |
| Sound Insulation | Higher | Lower |
| Mold Resistance | Moderate | High |
| Environmental Impact | Higher recycled content | Lower recycled content |
R-Value Comparison: Cellulose vs Fiberglass
R-value measures how well insulation resists heat flow the higher the number, the better the thermal performance per inch. Cellulose typically delivers 3.2–3.8 per inch, while fiberglass blown-in insulation delivers 2.2–2.7 per inch. That means cellulose can reach a given R-value with less material depth than fiberglass.
In practical terms, a properly filled 2×4 wall cavity can reach up to R-15 with cellulose. For attics in the Pensacola area, most homes should target R-30 to R-38.
How Much R-Value You Actually Need in a Gulf Coast Attic
Because Northwest Florida sits in a warmer climate zone, code-minimum requirements are lower here than in northern states but reaching R-30–R-38 in your attic still meaningfully reduces cooling costs during the long, humid summer months. You need to understand fiberglass insulation setup from the scratch.
Cellulose vs Fiberglass Blown-In Insulation for Attics
Attics are where this comparison matters most, since both materials are most commonly blown into open attic spaces rather than closed wall cavities.
In humid, coastal climates, fiberglass tends to be the safer default for unventilated or poorly ventilated attics, since it resists moisture better and is less prone to supporting mold growth, a topic we cover in more depth in Best Insulation Types for Humid Climates. Cellulose, when it absorbs moisture, can compact and lose R-value faster than fiberglass but when the attic is properly vented and sealed, cellulose still performs well even in moderately humid conditions according to Energy Stars information guide.
In retrofit and irregular attic spaces, cellulose has an advantage: it conforms tightly to joists, wiring, and odd angles, cutting down on the small air gaps that fiberglass can leave behind. This is also where cellulose’s superior air-sealing shows up most, and it’s a big part of why reducing noise with insulation tends to favor cellulose over fiberglass in shared-wall situations.
Bonus Tip: Whichever material you choose, pair it with proper attic ventilation and, where recommended, a vapor barrier this matters more for long-term performance than the R-value difference between the two materials.
Cost Comparison: Cellulose vs Fiberglass Blown-In Insulation
Fiberglass blown-in insulation is generally the lower-cost material up front, since it requires less processing than treated cellulose. However, because cellulose achieves a higher R-value per inch, you may need less material by volume to hit the same target R-value, which can narrow the price gap depending on your attic or wall depth.
Coverage also differs significantly by weight: a 30 lb bag of cellulose typically covers roughly 15–20 sq ft at R-19, while the same weight of fiberglass covers a much larger 60–70 sq ft at R-19, since fiberglass is far less dense.
Which Is Better: Cellulose or Fiberglass Blown-In Insulation?
There’s no single winner it comes down to your building and priorities:
- Choose fiberglass if your home is in a high-humidity area, has limited attic ventilation, or you want a material that won’t settle or lose R-value over time.
- Choose cellulose if you’re retrofitting an older home with irregular cavities, want the best air-sealing performance, or sound dampening between floors is a priority.
- Sustainability matters to you cellulose has significantly higher recycled content, a point we expand on in Environmental Benefits of Insulation.
- Longevity without maintenance matters more fiberglass holds its shape and R-value longer without settling.
- Allergies or respiratory sensitivity cellulose generally causes fewer irritation issues than fiberglass fibers.
Installation and Maintenance Insights
Cellulose’s ability to seal gaps and irregular cavities reduces air leakage and improves energy retention, but it settles over time and may need reapplication after 10–15 years. Fiberglass holds its shape better and typically doesn’t require the same reapplication schedule, but it doesn’t provide the same air-sealing without additional sealing work.
One thing worth knowing as a homeowner: installation quality is harder to verify with fiberglass than with cellulose. Under-filled fiberglass can look “fluffed up” to the right depth without actually reaching the rated R-value, while under-installed cellulose visibly deflates and settles quickly, which tends to expose a poor installation sooner. This is one of several reasons professional installation and follow-up inspection matter more than the insulation material itself if your current insulation is old or was poorly installed, our team can assess it before a fresh install.
Get Expert Insulation Guidance
Not sure which insulation is right for your attic or walls? Our technicians will assess your home’s climate exposure, current insulation levels, and budget, and recommend the material that actually fits your building not just the one that’s easiest to sell.
Call now: (850) 429-4969 or email; [email protected].
Frequently Asked Questions
Does cellulose insulation absorb moisture?
Yes. Cellulose can absorb moisture, which may cause it to compact and lose some R-value. It’s borate-treated to resist mold, but proper attic ventilation and vapor barriers are still recommended in humid climates.
Can you put cellulose over fiberglass insulation?
Yes, cellulose can generally be blown in over existing fiberglass to add R-value, as long as the fiberglass isn’t wet, moldy, or already compromised. A quick inspection first is recommended.
Does cellulose insulation attract pests?
No the borate treatment used in cellulose deters most common pests.
Can I use either type in my attic?
Yes, but the right choice depends on your attic’s ventilation, humidity exposure, and whether it’s new construction or a retrofit.
Is one type safer for people with allergies?
Cellulose generally causes fewer irritation issues than fiberglass, whose glass fibers can irritate skin and airways during handling.
Sources
- ENERGY STAR Recommended Home Insulation R-Values
