Open-cell spray foam expands dramatically, filling cavities completely, and cures soft and spongy — approximately R-3.7 per inch, excellent air sealing, good acoustic benefit, but vapor-permeable and not moisture-resistant. Closed-cell cures rigid and dense — approximately R-6.5 per inch, exceptional air and vapor barrier performance, and significant structural rigidity — at roughly twice the cost. For Utah: closed-cell is preferred in crawl spaces, rim joists, and unvented roof assemblies where moisture resistance and maximum R-value per inch matter; open-cell is effective in interior walls and conditioned attic decks where vapor permeability is acceptable.