Spray Foam vs. Fiberglass: Which Costs Less Over 10 Years?

Fiberglass wins on upfront price, every time. The more useful question is which option costs less once you factor in energy bills over a realistic ownership timeline — and that answer is less obvious than the sticker price suggests.

The Upfront Gap Is Real

Spray foam, especially closed-cell, runs meaningfully higher upfront than fiberglass batts for the same coverage area. There's no getting around that gap at installation time — it's the reason "spray foam is expensive" is the first thing most homeowners hear about it.

Where Fiberglass Loses Ground Over Time

Fiberglass's real-world performance is unusually sensitive to installation quality and doesn't stop air leakage the way spray foam does. Poorly installed batts — compressed, gapped, or settled over time — can perform at a fraction of their rated R-value, and that gap shows up as ongoing higher energy bills every month, not a one-time cost.

Running the 10-Year Math

Take a hypothetical $3,000 upfront cost difference between spray foam and fiberglass for a mid-size attic. If spray foam's air-sealing advantage saves even $30-$50 a month on heating and cooling (a realistic range in many climates for homes with previously poor air sealing), that difference closes the $3,000 gap somewhere between 5 and 8 years — with 2+ years of pure savings if you stay in the home longer than that.

Where Fiberglass Still Wins the 10-Year Math

In a mild climate with low energy costs, or a home that already had reasonably good air sealing before the insulation upgrade, the monthly savings gap narrows significantly, and fiberglass's lower upfront cost may never fully close. This is genuinely situation-dependent, not a universal answer either direction.

The Honest Conclusion

Spray foam is more likely to win the 10-year cost comparison in cold or hot climates with real energy costs, especially replacing genuinely leaky prior insulation. Fiberglass is more likely to remain the lower-total-cost option in mild climates or already-well-sealed homes. Use our cost calculator to get your own starting numbers, and run your specific energy costs against the difference.

Read the full cost breakdown, or get a free quote to compare real numbers for your home.