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Estimate the total installed cost of open-cell or closed-cell spray foam based on your project area, target R-value, and foam thickness.
Spray foam insulation costs vary significantly depending on foam type, thickness, and local labor rates. This calculator uses industry-standard pricing data to give you a realistic cost estimate per square foot and for your entire project.
If you've gotten a couple of quotes for spray foam and they came back wildly different, you're not imagining things. Spray foam pricing swings more than almost any other insulation type, and the reason isn't that contractors are guessing — it's that the cost depends on a handful of variables that most homeowners never think to ask about. Once you understand what's actually driving the number on your quote, the spread starts to make a lot more sense, and you're in a much better position to tell a fair price from an inflated one.
As a rough starting point, spray foam runs $1.00 to $1.50 per board foot for open-cell and $1.50 to $2.00 per board foot for closed-cell. That "board foot" unit trips people up, so it's worth pausing on — a board foot is one square foot of coverage at one inch of thickness. So if you need 3 inches of closed-cell foam in a wall cavity, you're not paying the per-square-foot price once; you're paying it three times over, once for each inch of depth.
Translated into what most people actually want to know — cost per square foot of wall or ceiling area at a typical installed thickness — you're generally looking at:
| Foam Type | Approximate Installed Cost Per Sq Ft | Typical Wall Cavity Application |
|---|---|---|
| Open-Cell Foam | $1.50 – $2.50 / sq ft | Standard 3.5-inch wall cavity |
| Closed-Cell Foam | $3.00 – $5.50 / sq ft | Same 3.5-inch cavity (applied thinner, priced higher per inch) |
That's a meaningful gap, and it's the first fork in the road when you're budgeting a project. A 2,000-square-foot home's walls and attic could reasonably cost anywhere from $6,000 on the low end with open-cell to well over $15,000 with closed-cell throughout, which is exactly why "spray foam costs X" answers you find online are often useless without knowing which type and how much square footage is actually involved.
The foam itself is a two-component chemical system — an "A side" (isocyanate) and a "B side" (polyol resin) — that gets mixed and expanded on-site through a heated spray rig. Material costs depend on:
Labor is where spray foam really separates itself from batt or blown-in insulation, and it's usually 40% to 60% of the total job cost — sometimes more on small or awkward jobs.
A few things drive labor pricing specifically:
Cross-section comparison of the two foam types.
The price gap between the two foam types isn't arbitrary — they're genuinely different products suited to different jobs, and picking the cheaper one isn't automatically the smart move.
Open-cell foam has a soft, spongy cell structure. It's lighter, less expensive, and expands more per set, which is why it's a popular choice for interior walls and attic underside-of-roof applications where cost matters and the space stays dry. It has a lower R-value per inch (typically around R-3.5 to R-3.6) and it's vapor-permeable, meaning moisture can pass through it — which is sometimes exactly what you want, and sometimes a problem, depending on the climate and assembly.
Closed-cell foam has a much denser, rigid cell structure. It runs roughly R-6 to R-7 per inch, meaning you get more insulating value out of less material thickness. It's also a vapor barrier and adds real structural rigidity to a wall or roof deck — which matters in high-wind regions where foam is sometimes used partly for its racking strength. It handles moisture and below-grade or exterior applications (rim joists, foundation walls) far better than open-cell, which is why it's usually the non-negotiable choice in those spots regardless of cost.
Beyond the open-cell/closed-cell decision, here's what tends to swing an estimate the most in practice:
Let's price out a realistic job: insulating an unfinished attic in a 1,800-square-foot ranch home, spraying the underside of the roof deck (a common approach for turning an attic into semi-conditioned space) rather than the attic floor.
$14,000 to $16,000 for this specific job. Swap to open-cell at the same thickness and you'd likely land closer to $7,000 to $9,000 instead — a real illustration of how much the foam type alone changes the bottom line, even before anything else about the job changes.
Keep in mind this is one specific scenario. A basement rim joist project (a few hundred square feet, closed-cell, easy access) might run under $1,500 total, while a full new-construction home with closed-cell throughout the exterior envelope can run well into five figures. There's no single "spray foam costs $X" number that applies broadly — it always comes back to type, thickness, area, and access.
Spray foam is genuinely one of the higher-performing insulation options available, but the pricing spread you'll see quoted is real and mostly explainable once you know what to look for. The type of foam, the thickness needed for your climate and assembly, the size and accessibility of the space, and whether fire-barrier work is required will account for almost all of the difference between a $2-per-square-foot quote and a $6-per-square-foot quote for what looks, on paper, like a similar job.
Use our free calculator to get an instant cost estimate based on your area, foam type, and target R-value.
Open Spray Foam Cost Calculator →This guide provides general educational and cost-planning information, not a contractor quote or professional engineering advice. Actual spray foam costs vary widely by region, project complexity, access conditions, and local labor rates. Always obtain multiple quotes from licensed, insured contractors and verify all code requirements — including fire barrier compliance — before proceeding with any insulation project.