Bob Bird, Bird Family HVAC & Insulation
September 19, 2026
If you’ve been spending any time researching how to make your home more comfortable—especially when Georgia’s summer heat turns your upstairs into the high desert —you’ve probably bumped into the great insulation debate: Fiberglass or Cellulose?
Ask three different contractors and you might get three different answers. Some will swear fiberglass is the only clean, modern choice. Others (like me!) will tell you cellulose is the undisputed king of home performance. We aren’t discussing spray foam in this article.
At Bird Family Insulation, we don’t play favorites for the sake of an argument. We install both.
Every home is built differently, every attic has its own quirks, and every homeowner has different priorities and budgets. Both materials do a fantastic job when installed correctly over a properly air-sealed attic floor. Here is an honest, behind-the-scenes look at how they compare, why one costs a little more than the other, and how to decide which one belongs over your ceiling.
Why We Love Blown-In Fiberglass
Modern blown-in fiberglass is a far cry from the itchy, pink batts your grandfather unrolled decades ago. Today’s loose-fill fiberglass insulation is engineered for clean, efficient coverage.
- Lightweight on Your Ceilings: Fiberglass has a very light (low) density. If you live in an older home with 1/2-inch or 3/8-inch ceiling drywall, or framing with wider 24-inch joist spans, fiberglass puts almost zero structural stress on your ceilings.
- Naturally Non-Combustible: Because it’s manufactured from spun molten glass and sand, fiberglass is naturally fire-resistant without requiring added chemical fire retardants.
- Dries Out Quickly: Fiberglass is moisture-resistant. If a roof leak or storm ever allows water into your attic, fiberglass won’t hold onto water permanently—once the leak is fixed, it generally dries right out.
- Lower Upfront Investment: Because fiberglass is lighter to transport and faster to install, it provides a high-performing thermal boundary at a very attractive price point.
Why We Love Stabilized Cellulose
Our cellulose insulation is made from post-consumer recycled paper fiber (about 85% by weight) that has been treated with natural all-borate minerals. It’s one of the highest-performing thermal materials available for retrofit attics.
- High-Density Air Blocking: While fiberglass insulates by trapping air in tiny glass pockets, cellulose works by blocking air movement with sheer density. In an Atlanta summer, when attic temperatures climb to 140°F, high-density cellulose significantly slows down unwanted heat transfer.
- Quieter Bedrooms: Because cellulose is high density, it serves as a terrific acoustic buffer. If you live near busy traffic, under a flight path, or simply want to muffle the sound of heavy downpours on the roof, cellulose quiets down the living space beneath it. If you’re tired of hearing the squeaky trash-truck & school bus brakes, or live around Atlanta’s airports, you want cellulose attic insulation!
- Treated with Borates: The natural borate treatment in our cellulose insulation does double duty. Not only does it give the material a Class-1 fire retardant rating, but pesky insects like spiders and roaches, and smaller rodents also strongly dislike it. In fact, the insects die. It creates an inhospitable environment for critters looking for a winter nesting ground. If you want to turn your attic into the Dead Sea, choose our all-borate cellulose insulation.
- Monolithic Blanket: When we install stabilized cellulose with our moisture-assisted equipment, the fibers interlock into a continuous, seamless blanket that hugs joists, wraps wiring, and fills odd framing cavities without gaps. Think of a highly effective wool army blanket!
What Does the Investment Look Like?
We believe in upfront, transparent pricing. Cellulose costs slightly more than fiberglass for a simple reason: mass and handling.
To reach a proper code-compliant R-value (like R-38 or R-49), cellulose requires significantly more physical weight and volume of material than fiberglass. If an attic upgrade requires 12 bales of fiberglass insulation, that same attic will need three times that amount in cellulose bales! That means more raw tonnage on our trucks, more staging, and specialized equipment to apply it smoothly.
To see how that looks in the real world, consider a typical 1,200 sq. ft. attic:
- R-38 Upgrade:
- An R-38 blown fiberglass upgrade would run around $2,100 (without accessories or adjustments).
- That same attic upgraded to R-38 stabilized cellulose would run about $2,340 (without accessories or adjustments).
- R-50 Maximum Efficiency Upgrade:
- For homeowners wanting our high-performance R-50 depth, fiberglass runs around $2,340 for a 1,200 ft2.
- Upgrading to R-50 stabilized cellulose runs about $2,580 for that same attic.
(Note: These figures represent straightforward insulation coverage. Every attic is unique, and quotes can vary depending on existing insulation removal, attic access, baffles, can light covers, material costs, or air sealing requirements.)
As you can see, the difference between the two materials is modest—usually just a few hundred dollars on an average home.
The Secret Most People Forget: Air Sealing
Here is the truth that matters more than the material debate: Neither fiberglass nor cellulose can do its job if air is leaking up through your ceiling. Building science teaches us the importance of stopping uncontrolled air trespassing & exchanging back and forth between your living space and attic.
Before a single pound of insulation is blown into your attic, the most critical step is air sealing. Plumbing chases, electrical wiring penetrations, top plates, and recessed lighting cans all act like open chimneys pulling conditioned air out of your home. Sealing those penetrations with expanding foam creates an airtight lid on your living space. Air sealing is especially vital if you are considering the more porous fiberglass insulation project. The built-in high density of stabilized cellulose literally adds the benefit of air sealing in its nature of blocking air flow.
Once that thermal boundary is sealed tight, whether you cap it with clean fiberglass or dense cellulose, your HVAC system won’t have to work nearly as hard.
How to Choose
- Go with Blown Fiberglass if: You want a clean, dependable thermal upgrade that keeps project costs as low as possible, or if your ceilings have structural or drywall weight limits.
- Go with Stabilized Cellulose if: You want maximum sound dampening, built-in air sealing performance, natural borate pest deterrence, and don’t mind a small upgrade investment for the added density.
Still not sure which one fits your attic best? That’s what we’re here for. Give Nicole a call or text, and she’ll gladly discuss your needs. And she’ll schedule an appointment for Beau or Chris Bird to climb up into your attic, measure your current levels, inspect your air ducts, and give you an honest recommendation that fits your home and your budget! Call or text now, 404-538-9168.
