What Is Closed Cell Spray Foam?
Closed cell spray foam (also called ccSPF or 2-lb foam) is a high-density spray polyurethane foam where the cells are fully closed — meaning they don't allow air or moisture to pass through. This makes it the highest-performing insulation available, combining exceptional R-value with vapor control and structural strength in a single application.
Key fact: At just 2 inches thick, closed cell spray foam delivers R-12 to R-14 — meeting or exceeding code requirements for basement walls in one pass.
Closed Cell R-Value Explained
Closed cell spray foam delivers R-6 to R-7 per inch — significantly higher than any other spray insulation and nearly double open cell foam. Here's what that means in practice:
| Thickness | R-Value | Best Application |
|---|---|---|
| 1 inch | R-6 to R-7 | Supplemental layer, rim joist |
| 2 inches | R-12 to R-14 | Basement walls, crawl space — meets code |
| 3 inches | R-18 to R-21 | Exterior walls, garage |
| 4 inches | R-24 to R-28 | Roof deck, commercial applications |
| 6+ inches | R-36 to R-42+ | Full attic conditioned space |
Closed Cell vs. Open Cell: Which to Choose?
Both types of spray foam insulate and air-seal, but they perform very differently. Choose closed cell when moisture control, maximum R-value per inch, or structural strength matters. Choose open cell when soundproofing is the priority and moisture is not a concern.
Choose Closed Cell When…
Below grade (basement, crawl space), exterior walls, rim joists, anywhere moisture is present, or when space is limited and you need maximum R-value per inch.
Choose Open Cell When…
Interior walls for soundproofing, interior attic rafters where vapor permeability is desired, or when budget is the primary concern.
See open cell guide →Best Applications for Closed Cell Spray Foam
- Basement walls — Resists moisture and provides R-12 to R-15 at 2–2.5 inches. No separate vapor barrier needed.
- Crawl space walls and floor — Encapsulates the crawl space, controlling moisture and stopping cold air infiltration.
- Rim joists — The single highest-ROI application. 2 inches of closed cell seals the rim joist permanently and adds R-12.
- Attic roof deck — Creates a conditioned, unvented attic. Ideal when HVAC equipment is in the attic.
- Exterior walls — New construction or retrofit. Eliminates thermal bridging and provides a complete air seal.
- Garage walls and ceiling — Insulates and air-seals attached garages, preventing CO infiltration into living spaces.
Closed Cell Spray Foam Cost in CT (2026)
| Project | Typical Cost (CT) | Notes |
|---|---|---|
| Rim joist (standard home) | $800 – $1,800 | Best ROI — 1–3 year payback |
| Basement walls | $1,500 – $4,000 | 2 inches, full perimeter |
| Crawl space encapsulation | $1,200 – $3,500 | Includes walls + floor joist area |
| Attic (conditioned) | $3,500 – $8,000 | Roof deck application, 4–6 inches |
| Exterior walls (retrofit) | $2,500 – $6,000 | 3 inches, injected or open wall |
CT Rebates Available: Eversource and UI customers may qualify for energy efficiency rebates on closed cell insulation projects. Ask EcoFoam how to apply — we help you claim every dollar available. See rebate guide →
Frequently Asked Questions
What is the R-value of closed cell spray foam per inch?
Closed cell spray foam delivers R-6 to R-7 per inch — the highest R-value of any spray-applied insulation. This is nearly double open cell foam (R-3.5/inch) and far exceeds fiberglass batts (R-2.9 to R-3.8/inch).
Does closed cell spray foam need a vapor barrier?
No. Closed cell spray foam at 2 inches or more acts as its own Class II vapor retarder, meeting building code requirements. A separate poly vapor barrier is not needed — and in many cases should not be added, as it can trap moisture between layers.
Can closed cell spray foam be applied in winter?
Yes, with proper equipment and technique. EcoFoam's heated spray equipment allows application in cold Connecticut winters. Substrate temperatures must be above 40°F for proper adhesion and expansion.
Does closed cell spray foam off-gas?
Like all spray foam, closed cell off-gases during and immediately after application. Occupants must vacate during spraying and for 24 hours after. Once fully cured, closed cell foam is inert and safe.