Open-Cell vs. Closed-Cell: The Real Cost Difference

Closed-cell foam costs roughly two to three times more than open-cell per board foot — a big enough gap that it's worth understanding exactly why, and when paying the premium is actually the right financial call.

The Raw Numbers

Open-cell typically runs $0.45-$0.65 per board foot installed. Closed-cell typically runs $1.00-$1.50 per board foot. On a straightforward per-board-foot basis, closed-cell is meaningfully more expensive — but board feet aren't the whole cost picture.

The Thickness Offset

Because closed-cell delivers roughly double the R-value per inch of open-cell (R-6 to R-7 versus R-3.5 to R-3.7), you generally need less thickness of closed-cell to hit the same target R-value. In a cavity depth-constrained space, this can partially offset the per-board-foot cost gap — you're buying fewer total board feet of the more expensive material to hit the same performance target.

Where Closed-Cell's Premium Pays for Itself

In cavities with real depth constraints — a 2x4 rim joist, a low-slope roof deck — closed-cell may be the only realistic way to hit code-minimum R-value at all, making the "cost comparison" somewhat moot: it's not open-cell vs. closed-cell, it's closed-cell vs. not meeting code. Closed-cell's vapor-barrier and structural properties at sufficient thickness also add real value in specific applications (below-grade, flood-prone areas) that open-cell simply can't provide regardless of thickness.

Where Open-Cell's Lower Cost Wins

In a standard 2x6 wall cavity with adequate depth, open-cell can usually hit a strong R-value target at meaningfully lower total cost, and its vapor permeability may be the more appropriate choice for the climate and assembly anyway (see our sister site's building-science content on vapor barrier physics). Paying the closed-cell premium in a cavity that doesn't need it is spending more without gaining assembly-relevant benefit.

The Real Decision Framework

The right question isn't "which is cheaper" in the abstract — it's "which one correctly performs the job this specific assembly needs, at the lowest cost that achieves that." A contractor recommending closed-cell everywhere by default, regardless of assembly, is optimizing for their own margin, not your budget.

See the full cost breakdown or use the cost calculator to compare both options for your specific project.