Side-by-side specs
| Spec | Fiberglass | Cellulose |
|---|---|---|
| R-value per inch | R-2.2–2.7 | R-3.6–3.8 |
| Cost per sq ft installed | $0.80–$2.50 | $1.00–$2.75 |
| Recycled content | 20–30% | 75–85% |
| Air resistance | Lower | Higher (denser) |
| Fire rating | Non-combustible | Class A with borate treatment |
Fiberglass
Pros
- Won't absorb water or grow mold
- Lighter — safer on older ceiling drywall
- Non-combustible, no fire retardants needed
- Widely stocked nationwide
Cons
- Lower R-value per inch
- Can lose performance if compressed
- Itchy to install — needs PPE
Cellulose
Pros
- Higher R-value per inch (R-3.6–3.8)
- Better air infiltration resistance
- Recycled paper content (eco-friendly)
- Dense-packs walls without netting in many cases
Cons
- Heavier — verify ceiling can hold it
- Treated with borate fire retardant (may smell briefly)
- Settles ~15% in attic blow
Which should you pick?
- Older home with fragile plaster ceilings: Go with Fiberglass. Lighter weight is safer.
- Dense-packing existing walls: Go with Cellulose. Cellulose's density blocks air leakage and conforms to cavities.
- Hot, humid climate near the coast: Go with Fiberglass. Fiberglass doesn't hold moisture if humidity spikes.
Frequently asked questions
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