Home › Insulation · Updated June 2026
Spray Foam vs. Fiberglass Insulation (2026): Cost, Lifespan & Which to Choose
Spray foam and fiberglass both add thermal resistance, but they work differently: fiberglass is a low-cost batt or blown-in material, while spray foam expands to fill gaps and also air-seals. The decision usually comes down to budget versus performance — fiberglass is far cheaper, but spray foam packs more R-value per inch and stops air leaks that fiberglass alone can't.
Side-by-side comparison
| Factor | Spray foam | Fiberglass |
|---|---|---|
| Upfront cost (installed) | ~$2,360 avg job | $300 – $600 avg job |
| R-value per inch | Closed-cell ~6 – 7 | ~3.1 – 3.8 (batts) |
| Air sealing | Expands to seal gaps (closed-cell air-seals) | Doesn't air-seal on its own |
| Moisture / mold | Closed-cell is watertight | Loses R-value if it gets wet |
| Relative cost | 4 – 8× fiberglass | Most economical insulation |
| Installation | Pro install recommended | DIY-accessible |
| Best for | Finished/hard-to-reach areas, air-sealing | Open framing on a budget |
Figures are typical national ranges — your numbers depend on your home and local market.
Pros & cons
Spray foam
Pros
- High R-value per inch (closed-cell ~6–7)
- Air-seals cracks and voids fiberglass can't
- Closed-cell is watertight, resists moisture
- Great for finished or hard-to-reach areas
Cons
- Far more expensive (4–8× fiberglass)
- Careful application; pro install recommended
- DIY kits rarely economical for larger jobs
Fiberglass
Pros
- Most economical insulation option
- Widely available and DIY-friendly
- Good R-value for the price (~3.1–3.8 / inch)
- Long-lasting when kept dry
Cons
- Lower R-value per inch than spray foam
- Doesn't air-seal — air leaks pass through
- Loses effectiveness if it gets wet
- Less effective in irregular cavities
How to choose
For open, accessible framing on a budget, fiberglass gives you solid R-value at the lowest cost. Choose spray foam — especially closed-cell — when you need to air-seal, insulate finished or irregular spaces, or maximize performance per inch, and you can absorb the higher upfront cost.
See the full cost breakdown
Frequently asked questions
It can be where air-sealing and tight spaces matter, since spray foam both insulates and seals; for straightforward open cavities on a budget, fiberglass is usually the better value.
Closed-cell spray foam reaches about 6–7 per inch versus roughly 3.1–3.8 per inch for fiberglass batts — close to double.
Fiberglass is fairly DIY-friendly, but spray foam needs careful application and is generally best left to professionals.
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