Spray Foam vs. Fiberglass Insulation: Is the Upgrade Worth It?

The EPA estimates that sealing air leaks and adding insulation cuts heating and cooling costs by about 15% on average — and the Department of Energy puts the typical whole-home savings from air sealing plus insulation at roughly $200 to $600 a year, depending on home size, climate, and energy rates. In Indiana (Climate Zone 5), where heating dominates energy bills, the colder climate pushes savings toward the higher end.

It is not recommended. Fiberglass batts should be removed before applying spray foam. Leaving fiberglass in place can trap moisture between the two materials, reduce the spray foam's adhesion to the substrate, and prevent proper inspection of the cavity. Removal adds cost but ensures the spray foam performs as designed.

Fiberglass is not inherently bad — it's a proven thermal insulator that has been used successfully for decades. Its limitations are air sealing (it has none), moisture performance (it degrades when wet), and longevity (it sags and loses R-value over 15 to 25 years). In applications where air sealing and moisture resistance are not critical, fiberglass can be adequate.

Spray foam insulation lasts the life of the building without settling, sagging, or losing R-value. Fiberglass batts typically begin degrading after 15 years and should be replaced every 15 to 25 years to maintain rated performance. Over a 50-year period, you would likely replace fiberglass at least twice while spray foam remains intact.

Yes. Because spray foam creates a complete air seal, it reduces the pathways through which outdoor allergens, dust, pollen, and pollutants enter the home. Homes with comprehensive air sealing have fewer avenues for outdoor contaminants compared to fiberglass, which allows air — and everything it carries — to pass through freely.

Older homes often benefit the most from spray foam because they tend to have the worst air leakage. Homes built before 1980 commonly have little or no air sealing. The EPA estimates that sealing and insulating cuts heating and cooling costs by about 15% on average, and the leakiest older homes tend to land at the higher end. Because the savings are larger where leakage is worst, the payback period for older homes is often shorter than for newer construction.

Commercial buildings typically see an even stronger return from spray foam than residential. Higher air infiltration loads from frequent door openings, complex rooflines, and large HVAC systems mean the air-sealing benefit has a bigger impact. The EPA's seal-and-insulate estimate is about 15% on heating and cooling for a typical building, and commercial envelopes with heavy air infiltration often benefit more — the bigger the leakage problem, the bigger the savings.