Closed-cell is worth the premium ($1.50-$2.50 per board foot vs $0.50-$1.20 for open-cell) wherever vapor barrier matters: rim joists, crawl-space walls, basement walls, and roof decks in conditioned-attic designs. For attic floors and interior partition walls, open-cell delivers equivalent functional performance at less than half the cost.
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The cost-benefit decision is location-by-location in the house. The three places where closed-cell premium is justified. (1) Rim joist and band joist: closed-cell creates an integrated vapor barrier at the worst air-infiltration point in pre-1995 Cincinnati homes. The board-foot count is small (a typical 2,500-sqft home rim joist is 100-150 board feet) so the absolute price difference is modest, $150-$300, well worth the vapor-barrier integration. (2) Crawl-space walls and basement walls: closed-cell at 2+ inches provides the vapor barrier required by IRC Class III when applied below grade. Open-cell does not function as a vapor retarder; using it below grade in Cincinnati Climate Zone 4A leads to moisture problems. The square-footage here can be significant; expect to pay $1,500-$4,000 closed-cell vs $700-$2,000 open-cell, but the open-cell choice is the wrong product. (3) Roof deck in a conditioned-attic design: closed-cell at the underside of the roof deck maintains the vapor-control integrity needed to bring the attic inside the conditioned envelope. The two places where open-cell is the right answer. (1) Attic floors with vented attic above: open-cell at R-3.7 per inch delivers required R-49 in 13-14 inches, the standard Climate Zone 4A retrofit spec, at meaningfully lower cost than closed-cell. The vapor permeability is desirable here so attic moisture can move out rather than back into the conditioned space. (2) Interior partition walls for sound dampening: open-cell adds 5-7 STC to a 2x4 cavity at low cost; closed-cell adds only 2-4 STC and costs 3x more. Real-world Cincinnati pricing: a hybrid whole-home foam project using closed-cell at the rim joist and crawl walls plus open-cell at the attic floor and interior partitions saves $2,000-$5,000 compared to all-closed-cell, with zero performance loss at the application points that matter.