Open-cell vs. closed-cell spray foam compared in a stud cavity
Closed-cell packs nearly 2× the R per inch of open-cell and adds air, water and vapor control plus rigidity (rim joists, roof decks, below grade). Open-cell is lighter, vapor-open, cheaper per R — but interior-only.
What this diagram shows
Two stud cavities filled with spray foam compared side by side. Open-cell ½-pound foam is R-3.6 per inch, light at 0.5 pounds per cubic foot, vapor-open so it can dry, not structural, interior-only, and gives the most R-value per dollar. Closed-cell 2-pound foam is R-6.5 per inch — nearly double — at 2 pounds per cubic foot, acts as an air and water barrier and a vapor retarder at 1.5 inches or more, adds rigidity, is flood-rated, and is used at rim joists, roof decks, and below grade, but it costs more.
Spray Foam Calculator
Spray foam take-off — board-feet, kit count, R-value, IECC compliance, vapor class. Open vs closed-cell. IRC R806.5 / R702.7 callouts. Free.
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