Closed-cell foam: R-7 per inch + air barrier + vapor barrier. Fiberglass: R-3.5 per inch + no air seal. Cellulose: R-3.7 per inch + minimal air seal. Foam outperforms both per inch and as an air barrier.
More detail
In Cincinnati climate (IECC Zone 4A), the comparison favors foam in three dimensions. (1) Per-inch thermal performance: 2 inches of closed-cell foam delivers R-14 in a cavity that holds R-7 of fiberglass. For a 2x4 wall cavity (3.5 inches deep), closed-cell delivers R-21 versus fiberglass batt R-12 to R-13. (2) Air sealing: foam fills cavity edges, around penetrations, and behind electrical boxes. Fiberglass and cellulose require separate caulking, gasketing, and detailing to achieve equivalent air seal. Real-world blower-door tests on otherwise-identical homes typically show foam-insulated wall assemblies leak 30-50% less air. (3) Longevity: foam does not settle, sag, or compress. Fiberglass batts compress under their own weight over decades and lose effective R-value. Loose-fill cellulose settles 10-20% over its installed life. The cost differential (foam is roughly 2-3x cellulose per equivalent R-value) is offset over 4-7 years of utility savings in Cincinnati. Cincinnati comparison context: at typical 2026 utility rates and local construction costs, the long-term cost of foam (per dollar saved over the building lifetime) typically beats fiberglass and cellulose for all but the shortest-tenure homeowners. Households planning to stay under 5 years may not see full payback; households planning to stay 7+ years almost always do. The non-financial benefits (comfort, air-quality, sound dampening) accrue regardless of tenure.