Quick Comparison
Open cell: ~R-3.7/inch, soft and spongy, lower cost, lets moisture pass. Closed cell: ~R-7/inch, rigid, higher cost, acts as a vapor barrier.
When We Use Open Cell
Attic rooflines, interior walls for sound, and large cavities where you need full expansion at the lowest cost per square foot.
When We Use Closed Cell
Crawl spaces, metal buildings, exterior walls in tight cavities, and anywhere moisture or structural strength matters.
What We Recommend in Chattanooga
For most homes here we use closed cell in the crawl space and on rim joists, and either type at the attic depending on budget. Humidity is the deciding factor — and Chattanooga has plenty of it.