What R-value does open cell spray foam provide?

Open cell spray foam delivers R-3.7 per inch. At 5.5 inches in a 2x6 rafter bay, that gives you R-20.35. In a 2x4 wall cavity at 3.5 inches, you get R-12.95. These values meet Oklahoma code requirements through either prescriptive or performance path compliance.

Can open cell foam get wet?

Open cell foam is vapor permeable, meaning moisture can pass through it rather than getting trapped. If a roof leak occurs, water moves through the foam and shows up on the ceiling below — you see the problem and fix it. Closed cell hides leaks. In Oklahoma's Climate Zone 3, open cell does not require a vapor retarder per IRC R806.5, which is one reason it works well in our attics.

Is open cell spray foam good for soundproofing?

Open cell foam is significantly better at sound dampening than closed cell. Its soft, flexible structure absorbs sound waves rather than reflecting them. We install it regularly in interior partition walls, home theaters, bedrooms above garages, and anywhere noise transfer is a concern.

How does open cell compare to closed cell on cost?

Open cell runs roughly 30-40% less per square foot than closed cell at comparable coverage. Because it expands to fill the full cavity in one pass, labor is efficient. For attic roof decks and interior walls where moisture resistance is not the primary concern, open cell gives you strong thermal performance at a lower cost.

Open Cell Spray Foam Insulation

What Open Cell Spray Foam Actually Is

Open cell spray foam is a half-pound density product (~0.5 lb/ft³) that expands roughly 100x when applied. The cells in the cured foam are open, creating a soft, sponge-like structure that traps air. That structure is what gives it two properties that matter in Oklahoma homes: thermal resistance at R-3.7 per inch and real sound dampening.

It is not a vapor barrier. It is vapor permeable. In Oklahoma’s Climate Zone 3, that is not a problem — it is an advantage. We will get to why.

Where Open Cell Belongs in Oklahoma

Attic Roof Decks

The most common application we install in the Oklahoma City metro is open cell foam sprayed to the underside of the roof deck. At 5.5 inches between 2x6 rafters, you get R-20.35. Oklahoma adopts the 2009 IECC, which calls for R-30 in ceilings. That number applies to flat attic floors with blown insulation above. When you move the thermal boundary to the roof deck and create an unvented attic assembly, you file a REScheck using the performance path, and the home passes as a system — not component by component.

Per IRC Section R806.5, unvented attic assemblies in Climate Zones 1 through 3 do not require a vapor retarder when using air-impermeable insulation (spray foam qualifies). That makes open cell a clean, code-compliant option for Oklahoma attics without adding poly sheeting or vapor retarder paint.

The practical benefit: your HVAC ductwork and air handler now sit inside conditioned space. In an Oklahoma summer where attic temperatures hit 140-150 degrees, that alone changes how your system performs.

Interior Walls

Open cell fills the full 3.5-inch cavity of a 2x4 wall in one pass, delivering R-12.95 and sealing every gap, wire penetration, and outlet box in the process. For interior partition walls — between bedrooms, around bathrooms, in media rooms — the sound dampening is the real value. Open cell absorbs mid-range frequencies (conversation, TV, music) far better than fiberglass batts.

Where It Does Not Belong

Open cell foam should not go in crawlspaces, below grade, rim joists exposed to exterior conditions, or anywhere subject to flooding or sustained moisture contact. It absorbs water. Those applications call for closed cell.

How We Install It

Open cell is sprayed as a two-component liquid that expands and cures in seconds. We overspray slightly past the framing depth, then screed (shave) it flush with the studs or rafters. The result is a uniform, airtight layer with no gaps, no voids, and no compression.

Typical attic roof deck: one day for most residential homes. We mask off anything that should not get foam on it, protect the ridge vent area if applicable, and clean up overspray before we leave.

The Air Sealing Factor

Here is something that gets overlooked: the R-value number is only part of the equation. Open cell spray foam is also an air barrier. It seals the building envelope in a way that fiberglass batts physically cannot. Air leakage is responsible for a significant share of energy loss in Oklahoma homes — often more than conductive heat transfer through the insulation itself. When you combine thermal resistance with air sealing in a single product, the real-world performance exceeds what the R-value alone suggests.

Bottom Line

Open cell spray foam is a proven, cost-effective insulation for attic roof decks and interior walls in Oklahoma. It meets code, it air seals, it dampens sound, and it does not trap moisture in a climate zone where trapping moisture is the wrong move. We install it every week across the OKC metro, and it does exactly what it is supposed to do.