Spray foam, explained
Open-cell vs. closed-cell, where each one earns its premium, and where cellulose is the better answer.
What you'll learn
- The R-value difference (open-cell R-3.7/in vs. closed-cell R-6.5/in)
- When closed-cell is worth the premium (rim joists, unvented decks)
- When open-cell wins (interior walls, sound, lower cost)
- When cellulose beats both spray foams on cost-per-R
Step by step
- Identify the assembly (vented attic floor, unvented roof deck, wall cavity, rim joist).
- Determine if vapor control matters in that location.
- Calculate cost-per-R for each candidate product.
- Pick spray foam where air-seal-plus-insulation in one step matters.
- Pick cellulose for attic floors where loose-fill performs as well at a fraction of the cost.
Safety note
If a contractor recommends spray foam for every assembly without explaining why, get a second quote. Most homes need a mix.
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