Open-Cell vs Closed-Cell Spray Foam: Which Does Your Arizona Home Need?

If you're researching spray foam insulation, you'll hit this question fast: open-cell or closed-cell? They're both "spray foam," but they perform differently, cost differently, and belong in different parts of your home. Pick the wrong one and you either overspend or under-protect.

Here's the plain-English breakdown we walk every homeowner through before we spray a single bay.

The core difference: cell structure

Spray polyurethane foam is made of millions of tiny cells (bubbles). In open-cell foam, those cells are deliberately broken open, making the foam soft, spongy, and full of air. In closed-cell foam, the cells stay sealed and packed tight, making the foam rigid, dense, and impermeable.

That one structural difference drives everything else — R-value, cost, moisture behavior, and where each foam belongs.

Closed-cell spray foam: the premium performer

Closed-cell is the dense, high-end option. Its standout properties:

• Highest R-value available — roughly R-6.5 per inch, about twice the insulating power of open-cell per inch.
• A built-in vapor barrier — it blocks moisture and air, which makes it the right choice anywhere water or humidity is a concern.
• Structural strength — because it's rigid and bonds to framing, it measurably stiffens walls and roof assemblies.
• Higher cost — it uses more material and more chemistry per board foot, so it runs more per square foot.

Closed-cell shines in crawl spaces, roof decks, metal buildings, basements, rim joists, and anywhere condensation or moisture is a factor. In the Arizona desert, it's often the right call for an unvented (conditioned) attic and for sealing a damp crawl space for good.

Read more: Closed-Cell Spray Foam.

Open-cell spray foam: the cost-effective air seal

Open-cell is lighter and significantly less expensive. Its strengths:

• Great R-value for the money — roughly R-3.6 to R-3.9 per inch, at a lower cost per board foot than closed-cell.
• Outstanding air sealing — it expands aggressively and fills every gap, which is the whole point of choosing foam over fiberglass.
• Excellent sound dampening — its soft, air-filled structure absorbs noise, making it ideal for interior walls and ceilings.
• Not a vapor barrier — it allows some vapor transmission, so it's the wrong choice for wet or moisture-prone areas.

Open-cell is the smart pick for vented attic floors, interior partition walls, sound-rated rooms, and large surface areas where you want foam's air-sealing performance at a lower price.

Read more: Open-Cell Spray Foam.

Side-by-side at a glance

| Property | Closed-Cell | Open-Cell | |----------|------------|-----------| | R-value per inch | ~R-6.5 | ~R-3.6–3.9 | | Cost | Higher | Lower | | Vapor barrier | Yes | No | | Air seal | Excellent | Excellent | | Best for | Roofs, crawl spaces, metal buildings, moisture zones | Attic floors, interior walls, sound dampening |

You don't have to pick just one

Here's the part most companies won't tell you: a well-designed insulation job often uses both. Closed-cell on the roof deck and crawl space where moisture and max R-value matter; open-cell on interior walls and ceilings where cost and sound matter. That's how you get premium performance where it counts without paying premium prices everywhere.

How we help you decide

There's no single "best" foam — only the best foam for each space in your home, your budget, and your goals. During a free walkthrough we inspect the attic, walls, and crawl space, look for moisture and air-leakage issues, and recommend the right material for each zone. We won't push closed-cell where open-cell is the smarter buy, and we won't talk you out of it where closed-cell is genuinely worth it.

Curious what your home actually needs? Get a free estimate and we'll tell you — honestly — which foam goes where.