Fiberglass vs. Cellulose vs. Spray Foam:
Which Material Fits Your Home?
Do not spend on insulation until you understand the cost, performance, air-sealing tradeoffs, and best use cases.
| Material | R-Value / Inch | Cost | Best For |
|---|---|---|---|
| Fiberglass Batts | 3.1 - 3.4 | $ (Low) | DIY projects, open walls |
| Blown-in Cellulose | 3.5 - 3.8 | $$ (Medium) | Attic floors, filling gaps |
| Spray Foam (Closed) | 6.0 - 7.0 | $$$$ (High) | Roof decks, air sealing |
1. Fiberglass: The Standard Choice
Fiberglass is the most common insulation material in North America. Made from spun glass fibers, it usually comes in rolls ("batts") or loose-fill.
- Pros: Widely available, fire-resistant, cheapest option.
- Cons: Itchy to handle, leaves gaps if not installed perfectly, loses R-value when compressed.
2. Cellulose: The Eco-Friendly Contender
Cellulose is made from recycled paper products treated with fire retardants. It is typically blown into attics using a machine.
- Pros: Higher R-value than fiberglass, fills irregular gaps well, eco-friendly.
- Cons: Can settle over time, holds moisture if a roof leaks.
Pro Tip: Air Sealing First
Before adding fiberglass or cellulose, seal major air leaks around pipes, wiring, and top plates. These materials slow heat flow but do not stop airflow by themselves.
3. Spray Foam: The High-Performance Option
Spray polyurethane foam expands to fill cavities. Closed-cell foam cures rigid and water-resistant, while open-cell foam stays softer and less dense.
- Pros: Highest R-value per inch, creates an air barrier, adds structural rigidity.
- Cons: Expensive, professional installation only, temporary off-gassing during cure.
Which One Should You Choose?
The answer depends heavily on your climate zone.
- Hot climates (Zones 1-2): Miami or Phoenix. Moderate R-values plus good air sealing can keep attic heat out effectively.
- Cold climates (Zones 5-7): Chicago or Minneapolis. Thick attic coverage and aggressive air sealing matter much more.
Stop Guessing. Start Calculating.
Not sure whether your attic is under-insulated? Use the calculator to compare your current depth against the right retrofit target.
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