What Is Closed-Cell Spray Foam?
Closed-cell spray polyurethane foam cures into a rigid material with a density around 2 lb/ft³ in which every cell is sealed and gas-filled. That structure is why it insulates so well per inch (R-6 to R-7), why water cannot soak into it, and why it adds measurable racking strength to walls and roofs. At 1.5 inches or more it qualifies as a Class II vapor retarder, so in most Bay Area assemblies no separate vapor barrier is needed.
USA Spray Me installs closed-cell foam for homeowners, builders, property managers and facility owners throughout San Francisco, the Peninsula, East Bay, South Bay and North Bay.
Where Closed-Cell Foam Makes the Most Sense
- Crawl spaces — fog-belt crawl spaces in the Sunset, Richmond, Daly City and Pacifica stay damp year-round; closed-cell foam on the subfloor or stem walls stops cold floors and mold.
- Basements and below-grade walls — the only insulation that tolerates contact with concrete and incidental moisture.
- Exterior walls — maximum R-value in a 2×4 cavity (R-21 at 3.5") for Title 24 compliance without furring out the wall.
- Metal buildings, barns and shipping containers — bonds directly to steel, stops condensation drip and adds rigidity.
- Cold storage, walk-ins and wine rooms — continuous insulation with no thermal bridging.
- Rim joists and band joists — the leakiest joint in the house, sealed in one pass.
- Flash-and-batt hybrids — 1–2 inches of closed-cell for air sealing and vapor control, topped with batts or blown-in to hit the R-value at lower cost.
Closed-Cell Foam Performance at a Glance
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| Property | Closed-cell SPF |
|---|---|
| R-value per inch | R-6.0 – R-7.0 (aged) |
| Density | ~2.0 lb/ft³ |
| Water absorption | < 2% — will not wick or hold water |
| Vapor permeance | Class II vapor retarder at 1.5"+ |
| Air barrier | Yes, at 1"+ |
| Structural contribution | Adds up to 2–3× wall racking strength |
| Service life | 30+ years / life of the building |
| Typical installed cost | $1.50 – $2.50 per board foot |
Closed-Cell vs. Open-Cell: Choosing Correctly
Open-cell foam is cheaper per R and excellent for sound, so we often recommend it for attic roof decks and interior walls. Closed-cell wins wherever moisture, limited cavity depth, structural loads or below-grade conditions are involved. Many Bay Area projects use both — closed-cell in the crawl space and rim joists, open-cell in the attic — and our free inspection is where we work out that mix with you.
Installation, Cure Time and Safety
Closed-cell foam is applied in lifts of about 2 inches to control exotherm, so a 3.5-inch wall takes two passes. Most residential crawl-space or wall projects finish in a day; metal buildings and commercial spaces in 2–5 days. The foam is tack-free in seconds and fully cured in roughly 24 hours, during which the space should be vacated and ventilated. We are licensed by the CSLB (#1058008), bonded and insured, and every installation carries a written workmanship warranty.
Free on-site inspection and written quote for closed cell insulation anywhere within 100 miles of San Francisco.
Recent Closed Cell Insulation Projects
Where We Offer Closed Cell Insulation
USA Spray Me provides closed cell insulation throughout San Francisco, the Peninsula, South Bay, East Bay, North Bay and the Central Valley — every community within 100 miles of our Treasure Island headquarters, including:
