Closed-Cell vs. Open-Cell Foam: Which Is Right for a Coastal Florida Home?

The one-sentence version

Closed-cell foam seals and reinforces; open-cell foam breathes and quiets. For a coastal South Florida home, closed-cell is almost always the right call for the building envelope — and open-cell has a place inside.

Closed-cell spray foam

Closed-cell foam is dense — its cells are sealed shut, trapping gas inside. That gives it three properties that matter on the coast:

• Vapor barrier — it blocks moisture. In a Delray Beach waterfront home, this is the difference between a dry wall cavity and a mold farm.
• Structural reinforcement — closed-cell foam actually stiffens wall and roof assemblies. In hurricane country, that's not a gimmick.
• High R-value per inch — R-6.5+, so you hit Florida code R-30 in less than 5 inches.

Downside: it's more expensive, and it doesn't let a wall cavity dry out if moisture gets in behind it. That's why proper air-sealing and a FLIR inspection before install matter — you don't want to trap a leak.

Open-cell spray foam

Open-cell foam is softer and its cells are, well, open. Air moves through it slowly. That gives it different strengths:

• Vapor permeable — it lets a wall cavity breathe, which can be desirable in certain wall assemblies.
• Sound dampening — it's excellent for interior walls, media rooms, and between-floor sound control.
• Cheaper — roughly 60% the cost of closed-cell.

Downside: it's not a vapor barrier, it has lower R-value per inch (R-3.8), and it doesn't add structural rigidity. In a humid coastal attic, open-cell alone won't protect against moisture the way closed-cell will.

How we use them together

For a typical Boca or Delray coastal home:

• Attic roof deck / attic floor: closed-cell foam (vapor barrier, high R-value, moisture protection).
• Garage and exterior walls: closed-cell foam where moisture risk is high.
• Interior bedroom / media walls: open-cell foam for sound.
• Between floors: open-cell for footstep and sound control.

This is the stack that gives you a sealed, dry, quiet, energy-efficient coastal home.

The mistake to avoid

Don't let a crew talk you into open-cell in a coastal attic "to save money." In Boca's humidity, open-cell in the roof deck can absorb moisture over time and lose performance. If budget is the constraint, do closed-cell in the critical zones (attic, exterior walls) and skip the interior sound foam for now — you can add it later. Never downgrade the envelope.