Open Cell vs Closed Cell Spray Foam

Contractor's guide · Updated October 2026 · 7 min read

This is the question we hear on nearly every estimate: which foam should I get? The honest answer is that both are excellent products — they just solve different problems. Here's how open-cell and closed-cell spray foam actually compare, and how to choose for your home or building.

Side-by-Side Comparison

Open-Cell Spray Foam: The Air-Sealing Workhorse

Open-cell foam is lighter, softer, and significantly cheaper. Its cells are exactly what the name says — open — which makes it vapor-permeable and outstanding at absorbing sound. Where it shines:

• Attic floors: affordable, excellent air sealing, plenty of R-value at 5–6 inches.
• Interior walls: quiets room-to-room and neighbor noise dramatically.
• Irregular cavities: expands aggressively to fill odd voids in old framing.

Its limitation: because it's vapor-permeable and can absorb water, open-cell does not belong below grade, on roof decks exposed to moisture drive, or anywhere bulk water is a risk. For pricing context, see our Brooklyn cost guide.

Closed-Cell Spray Foam: The Premium All-Rounder

Closed-cell foam is dense, rigid, and roughly twice the R-value per inch. Its closed cells resist water, block vapor at sufficient thickness, and even add structural rigidity to wall and roof assemblies. It's the right call for:

• Basements & crawl spaces: moisture resistance is non-negotiable below grade — see our basement service.
• Roof decks (unvented attics): high R-value in limited rafter depth, plus vapor control.
• Exterior walls & coastal zones: flood and humidity resilience, from Canarsie to the Rockaways.
• Where space is tight: when you need R-13+ in 2 inches, nothing else does it.

The tradeoff is cost — closed-cell runs 60–100% more per board foot — and it's less effective at sound dampening than open-cell.

What We Recommend for NYC Homes

In practice, most Brooklyn and Queens projects use both: open-cell for the attic floor and interior walls where it's the best value, closed-cell for the basement, rim joists, and roof deck where moisture performance matters. A good contractor doesn't push one foam for everything — they match the product to the assembly. That's what our free estimates do.

Common Myths

"Closed-cell is always better."

It's better per inch, but not always better per dollar. For a vented attic floor, open-cell delivers the air sealing and R-value you need at nearly half the price. Spending double for closed-cell there buys you almost nothing.

"Open-cell causes roof rot."

Open-cell on an attic floor is perfectly fine. Problems arise only when it's misapplied — like open-cell directly on a roof deck in a cold climate without vapor management. Application matters more than the product.

"Spray foam makes the house too tight."

Tight houses need planned ventilation, and that's true of any good air-sealing work. In older NYC homes, we're typically bringing a sieve up to "reasonably tight" — not building a passive house. If your project warrants it, we'll discuss ventilation.

Related Reading

• Spray Foam Insulation Cost in Brooklyn (2026 Guide)
• Attic Insulation Brooklyn
• Basement & Crawl Space Insulation
• Residential Spray Foam Insulation Brooklyn