What makes closed cell different from open cell?

Density and cell structure. Closed cell foam is approximately 2.0 lb/ft³ — four times denser than open cell. The cells are closed and filled with blowing agent, giving it R-6.5 per inch compared to R-3.7 for open cell. At 1.5 to 2 inches thick, closed cell becomes a Class II vapor retarder (1 perm or less). It also adds measurable racking strength to wall assemblies. These properties make it the right choice anywhere moisture, structural loads, or limited cavity depth are factors.

How thick does closed cell need to be in walls?

In a 2x4 wall in Oklahoma (Climate Zone 3), 2 inches of closed cell delivers R-13, which meets the 2009 IECC prescriptive requirement. That leaves 1.5 inches of cavity space, which can remain empty or be filled with fiberglass for additional R-value. In a 2x6 wall, 3 inches of closed cell provides R-19.5 — exceeding the R-20 wall requirement under some code paths.

Does closed cell spray foam add structural strength?

Yes. Closed cell foam bonds to the substrates it is applied to and adds racking strength to wall assemblies. Studies from the National Association of Home Builders Research Center have documented increases in wall racking strength. This matters in metal buildings and post-frame structures where the foam is bonding directly to the metal skin and contributing to the overall rigidity of the envelope.

Is closed cell spray foam waterproof?

Closed cell foam does not absorb water. It has a closed cell structure that resists moisture absorption, and at 2 inches it functions as a Class II vapor retarder. This is why we use it in crawlspaces, below-grade walls, rim joists, and flood-prone areas. FEMA recognizes closed cell spray foam as a flood-resistant insulation material.

Closed Cell Spray Foam Insulation

What Closed Cell Spray Foam Is

Closed cell spray foam is a two-pound density product (~2.0 lb/ft³) with a rigid, closed cell structure. Each cell is sealed and filled with blowing agent, which is what drives the R-value to R-6.5 per inch — the highest of any common insulation material. At 1.5 to 2 inches of thickness, it crosses the threshold to become a Class II vapor retarder at approximately 1 perm.

It bonds to wood, metal, concrete, and masonry. It does not absorb water. It adds structural rigidity to whatever it is applied to. These are not marketing claims — they are physical properties of the cured product.

Where Closed Cell Belongs in Oklahoma

Crawlspaces

Crawlspace walls and rim joists are the primary residential application for closed cell in Oklahoma. The foam goes directly on the block or poured concrete walls and across the rim joist, creating a continuous air barrier and vapor retarder in one step. Two inches on the crawlspace walls provides R-13 and stops moisture migration from the soil and exterior. We cover this in detail on our crawlspace encapsulation page.

Rim Joists

The rim joist is the single leakiest component in most Oklahoma homes. It sits at the intersection of the foundation and framing — a seam that moves, cracks, and allows unconditioned air straight into the floor system. Two inches of closed cell on the rim joist seals it completely: air barrier, vapor retarder, and thermal break in one application.

Metal Buildings

Closed cell bonds directly to metal panels without fasteners or framing. That bond eliminates the air gap where condensation forms in metal structures. In Oklahoma, where summer humidity drives moisture toward the cooler interior surfaces of a metal building, that condensation control is not optional — it is the entire reason you insulate a metal building in the first place.

Below-Grade and Flood Zones

Any surface in contact with soil or subject to flooding needs insulation that does not absorb water. Closed cell foam meets FEMA standards for flood-resistant insulation. Fiberglass, cellulose, and open cell foam do not. For basement walls, below-grade stem walls, and structures in Oklahoma flood plains, closed cell is the correct material.

Exterior Walls — Limited Cavity Depth

In a 2x4 wall, you have 3.5 inches of cavity. Two inches of closed cell delivers R-13, meeting the 2009 IECC prescriptive R-value requirement for Climate Zone 3. That leaves room in the cavity for electrical and plumbing runs without compressing the insulation. In renovation work where you cannot change the framing depth, closed cell gives you code-compliant R-value in less space than any other option.

How We Install It

Closed cell is applied in lifts (passes) of no more than 2 inches at a time. Thicker applications require multiple passes with cooling time between them to prevent excessive exothermic heat. A typical 2-inch wall application is one lift. A 3-inch roof deck application is two lifts.

The foam is rigid when cured. It does not shrink, settle, or sag. It stays where we put it for the life of the structure.

When Closed Cell Is Not the Right Call

Closed cell costs more per board foot than open cell. In applications where moisture resistance and vapor retarder properties are not needed — interior partition walls, attic roof decks in Climate Zone 3 where open cell is code-compliant — you are paying for properties you do not need. We will tell you that. The right foam in the right location is better than the expensive foam everywhere.

What You Get

Closed cell spray foam is the highest-performing insulation we install. It delivers thermal resistance, air sealing, vapor retarder, moisture resistance, and structural reinforcement in a single product. Where those properties matter — and in Oklahoma, there are plenty of places they do — nothing else does the same job.