Fiberglass batts have R-3.5/inch and zero air-sealing. Closed-cell foam has R-7/inch plus air and vapor barriers in one product. Fiberglass also sags and degrades; foam lasts the lifetime of the home.
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Fiberglass batts have been the dominant residential insulation for 60+ years for one reason: cost. At roughly $0.30-$0.60 per sqft installed, batts are 4-7x cheaper than closed-cell foam per equivalent surface area. The performance gaps. (1) Air seal: fiberglass batts let air pass through them and around them; air leaks through cavity edges, around penetrations, and behind electrical boxes. Achieving equivalent air seal requires separate caulking, gasketing, and air-barrier detailing that bumps installed cost meaningfully and is rarely done well in retrofit. (2) Settling: batts compress under their own weight and from gravity, losing R-value over decades. (3) Moisture sensitivity: wet fiberglass loses R-value and can promote mold; closed-cell foam is impermeable. (4) Pest susceptibility: rodents nest in fiberglass; foam is harder to penetrate. The math favors foam for any home where the homeowner plans to stay 5+ years and value envelope performance, especially in Cincinnati Climate Zone 4 with its wide temperature swings. Cincinnati pre-1980 housing context: most Hyde Park, Norwood, Mariemont, and Madeira homes built before 1980 have R-7 to R-11 fiberglass batts in the walls (where they have any insulation at all) and R-12 to R-22 of compressed blown insulation in the attic. Upgrading to foam in those assemblies produces the largest absolute energy savings of any home modification short of HVAC replacement. Newer homes (post-1995) start from a better baseline and see proportionally smaller upgrade gains.