Fiberglass vs. Spray Foam Insulation

Fiberglass and spray foam both insulate, but they work in fundamentally different ways. Fiberglass slows heat by trapping air in fine glass fibers, while spray foam expands to fill and seal a space, blocking both heat transfer and air movement.

That difference — air sealing — is the heart of the comparison.

Spray foam reaches a higher R-value per inch and seals air leaks at the same time, which can make a big difference in a drafty home. Closed-cell foam even adds some structural rigidity and resists moisture.

Fiberglass has a lower R-value per inch and doesn't stop air leakage on its own, so it's usually paired with separate air sealing to perform its best. In a mild climate, well-installed fiberglass plus air sealing performs very capably.

Fiberglass is significantly cheaper and can sometimes be a DIY project. Spray foam costs considerably more and must be professionally installed with the right equipment and safety precautions.

That cost gap is the main reason many homeowners choose fiberglass — and get excellent results — reserving spray foam for situations where its air-sealing strength justifies the price.

Choose spray foam when air leakage is a major problem or you need high performance in limited space. Choose fiberglass when you want strong, cost-effective insulation and can pair it with proper air sealing.

A professional can evaluate your home and tell you honestly which option delivers the better value for your situation.