Open Cell vs Closed Cell Spray Foam
Two products, very different jobs — and why most metal buildings don't actually need closed cell
(405) 659-1046Spray foam comes in two forms: open cell (low-density, semi-rigid, expands roughly 100x its liquid volume) and closed cell (high-density, rigid, expands roughly 30x). They look similar going on the wall but behave very differently — and choosing the wrong one for the application either wastes thousands of dollars (closed cell where open cell would have done the job) or leaves real performance on the table (open cell where closed cell's specific advantages actually matter). Premier Insulation has been installing both products since 2006 and recommends whichever fits the job. This guide covers the real differences, where each one is the right answer, and the single most common (and most expensive) misconception in commercial spray foam: that metal buildings require closed cell.
If you've already decided you want spray foam and you're trying to figure out which type, this is the page for you. If you're still comparing spray foam to blown fiberglass more broadly, see our spray foam vs fiberglass comparison instead. See spray foam vs fiberglass instead →
TL;DR — When to Pick Each
Residential walls (new construction or remodel)
→ Open cellCosts roughly half what closed cell does, performs comparably for the application, dramatically better at sound dampening (a real-world benefit homeowners notice immediately). Premier's default for residential walls.
Attic conversion (foam the roof deck to create a conditioned attic)
→ Open cellLower weight (won't add unnecessary load to your roof framing), excellent thermal performance, sound dampening from road / weather noise. The standard for residential attic conversions in our climate.
Crawlspaces and floors over unconditioned space
→ Open cellVapor-permeable so trapped moisture can dry out, lighter weight, more cost-effective. We use open cell on virtually every residential crawlspace job.
Metal building (shop, pole barn, agricultural building)
→ Open cell + OSB on lower wallsThe big myth-buster — see the dedicated section below. Open cell matches closed cell on condensation control, vapor performance, and structural needs at half the cost, AND beats it on sound. The only thing closed cell wins is contact durability, which is solved cheaper by sheathing the lower 8 feet with OSB (which doubles as workshop wall surface for shelves/workbenches).
Stem walls / below-grade exterior basement walls
→ Closed cellThis is one of closed cell's clear-win applications. The high density and vapor-barrier properties handle the moisture loading from earth contact that would compromise open cell over time.
Underslab ductwork insulation
→ Closed cellSpecialized application requiring the high-density, low-permeability product. Open cell would not survive the slab moisture environment.
Commercial freezer / refrigerator / cold-storage spaces
→ Closed cellThe vapor-barrier properties are critical when you're maintaining a meaningful temperature differential against humid outside conditions. Open cell would allow moisture migration and condensation issues.
Exposed metal-building shop walls (no OSB sheathing planned)
→ Closed cellIf the foam itself is going to be the finished interior surface AND you want a ladder-resistant, dent-proof wall, closed cell's contact durability is the deciding factor. But honestly — most customers we walk through the math choose to add OSB sheathing instead and use open cell, because the savings more than pay for the OSB and you end up with a more workshop-functional wall.
Head-to-Head Comparison
| Category | Open Cell | Closed Cell |
|---|---|---|
| R-Value Per Inch | About R-3.6 per inch (R-38 = ~10.5 inches, R-49 = ~13.5 inches) | About R-7 per inch (R-38 = ~5.5 inches). Higher per-inch makes closed cell the only option for very shallow cavities where you can't fit enough open cell. |
| Density | Half-pound (0.5 lb/cubic foot). Semi-rigid, soft to the touch, slightly springy. The cell structure is open (unsealed) — which makes the cured foam vapor-permeable and excellent at absorbing sound, but at typical install thicknesses the foam still functions as an effective air barrier in practice (the 'air passes through' claim you'll see online overstates it dramatically). | Two-pound (2.0 lb/cubic foot). Rigid, hard surface, won't dent under moderate pressure. Cells are sealed, blocking air and water passage through the material. |
| Expansion Ratio | ~100× its liquid volume. Aggressive expansion fills every crack and gap in seconds — fewer passes needed for full coverage. | ~30× its liquid volume. Less aggressive, more controlled. Sometimes requires multiple passes (lifts) to reach full thickness. |
| Cost (per square foot) | Roughly half the cost of closed cell. The cost-effective choice for any application where it fits the requirements. | Roughly 2× the cost of open cell. Earned premium when its specific advantages (vapor barrier and contact durability primarily) genuinely matter for the application. |
| Air Sealing | Excellent. Expands aggressively and seals every gap as it cures — eliminates air infiltration as a heat-loss path. | Excellent. Same air-seal benefit. Both products solve the air-infiltration problem fiberglass can't address. |
| Vapor Permeability | Vapor-permeable. Allows moisture vapor to pass through. If it gets wet (e.g. roof leak), it dries out instead of trapping water against the structure. | Acts as a vapor barrier (Class II at typical thickness). Critical for stem walls, below-grade applications, and cold-storage spaces. Overkill for typical above-grade walls. |
| Sound Dampening | Excellent. The open-cell structure absorbs sound waves rather than reflecting them. Many homeowners specifically choose open cell for the noticeably quieter home (less road noise, less between-room transmission). One of the most-mentioned benefits in our customer feedback. | Modest. The rigid, dense structure reflects sound rather than absorbing it. Closed cell is NOT recommended when sound dampening is a priority. |
| Structural Rigidity | Negligible structural contribution. Stays flexible enough to accommodate typical building movement. | Adds measurable racking strength in laboratory tests. Real-world relevance is very limited on 99% of buildings — if you're genuinely concerned about structural integrity, that's a job for a structural engineer, not your insulation choice. (See the misconceptions section below for the honest take.) |
| Weight | Very light — adds minimal load to building framing. Safe to apply at full thickness on roof decks, ceilings, and overhead applications without concern. | Heavier (4× the density of open cell). Usually not an issue for typical applications, but worth considering on long-span roof decks or older framing. |
| Contact Durability | Soft surface — will dent if you lean a ladder into it or hit it with a tool. Needs to be covered (drywall, OSB, paneling, etc.) anywhere it's exposed to physical contact. | Hard, ladder-resistant surface. Stays as the finished interior surface in shop / commercial / agricultural applications without needing to be covered. |
| Lifespan | Designed to last the life of the building (80+ years). Doesn't degrade unless physically damaged. | Same — designed for the life of the building. |
| Indoor Air Quality (post-cure) | Odorless and inert within 24 hours of proper installation. Meets all current safety standards. | Same. Both products are safe and odorless once fully cured. The horror stories online are about jobs done with off-spec product or improper mix ratios — both avoidable with a qualified contractor. |
The Metal Building Question — Why Default to Closed Cell Is Almost Always Wrong
The conventional wisdom in commercial spray foam is that metal buildings require closed cell. It's repeated by sales reps, written into spec sheets, and assumed by most contractors. It's also wrong on the math AND wrong in practice — and we have years of repeat-customer evidence to back that up.
Where the Myth Comes From
Closed cell has four genuine advantages over open cell: condensation control, vapor barrier properties, structural rigidity, and contact durability. Three of those (condensation, vapor, structural) sound directly relevant to metal buildings — bare metal is a condensation magnet, the building flexes, and you don't want moisture problems. So sales reps default to closed cell and customers don't push back. That's how the myth stays alive.
Why It Falls Apart on Examination
On a typical metal building, open cell matches closed cell on condensation control (it air-seals just as effectively, which is what actually prevents condensation — not the foam's vapor barrier properties), has comparable vapor performance for the application (moisture vapor that does penetrate can dry to the inside instead of being trapped), and the structural rigidity benefit is largely irrelevant on a metal building that already has its own structural system (pre-engineered frame, purlins, girts). Open cell ALSO outperforms closed cell on sound dampening — a meaningful real-world benefit in an echo-prone metal-walled space. The only category where closed cell genuinely wins on a typical metal building is contact durability.
The Practical Solution: Open Cell + OSB on Lower Walls
Most metal-building owners want a workshop-functional interior anyway — a place to hang shelves, mount workbenches, screw in tool hooks. Bare exposed foam (whether open or closed cell) is a terrible surface for that. The solution most of our commercial metal-building customers use: open cell foam on the entire envelope, then OSB sheathing on the lower 8 feet of interior walls. The OSB protects the open cell foam from contact damage AND gives you a real working surface for everything you'd actually want to hang. The cost savings from open cell vs closed cell more than pays for the OSB.
The Real Proof: Repeat Customers
We have repeat commercial customers who used closed cell exclusively on multiple metal buildings for years before we did one open cell + OSB job for them. They haven't gone back since. These aren't first-time customers being upsold — these are contractors and shop owners who specifically chose closed cell for years and switched after experiencing both side by side. They're choosing the one that performs better and is more affordable at the same time.
When Closed Cell Is Still the Right Call on Metal
Two scenarios: (1) The customer specifically wants the foam itself to be the finished interior surface (no OSB, no drywall, no paneling) AND wants the ladder-resistant, dent-proof finish that only closed cell delivers. (2) Specialized applications like cold-storage metal buildings where the vapor-barrier properties are critical for the operating environment. Outside of those two scenarios, open cell + OSB is the better answer almost every time.
Common Misconceptions
Claim: “Closed cell is always better because it has higher R-value per inch.”
Reality: R-value per inch only matters if you're cavity-limited. In a typical 2x4 wall (3.5 inches deep) you can install ~12 inches' worth of R-value with open cell or ~24 inches' worth with closed cell — both massive overkill for a wall that only needs R-13 to R-21. Even cathedral ceilings (typically 2x10 or 2x12 rafters, 9-11 inches deep) have plenty of room for open cell to hit residential R-targets. The R-value-per-inch advantage really only matters in EXTREMELY shallow cavities — custom-insulated trailers, van / skoolie / RV conversions, container conversions, food trucks, and similar specialty builds where you've got 1-3 inches to work with and every R-point counts. For typical residential and commercial applications, both products easily exceed what the cavity needs.
Claim: “Closed cell is required for any application where moisture might be present.”
Reality: False. Closed cell is required for applications where moisture is CONSTANTLY present (below-grade walls, slab contact, cold-storage spaces). For typical above-grade walls and attics where occasional moisture might occur (roof leaks, condensation events), open cell is actually safer because it allows the moisture to dry out instead of trapping it against the structure.
Claim: “Closed cell adds structural strength that walls need.”
Reality: A laboratory test will absolutely confirm that closed cell adds measurable racking strength to a wall — that part's true. The real-world relevance on 99% of buildings? Essentially zero. If you're genuinely worried about your brand-new project's structural integrity, contact your general contractor — and maybe a lawyer — because insulation SHOULD NOT take the place of proper structural engineering. Could there theoretically be a narrow edge case where the exact wind-shear load that would have racked an open-cell-insulated wall but just barely doesn't rack a closed-cell-insulated one? Sure, in theory. The probability of that specific edge case lining up against your specific building is extremely low. Honest reality: if a tornado hits a building, or throws a 5,000-pound truck into it, the foam type doesn't matter — that building is getting damaged either way. Closed cell's added rigidity is real on a stress-test rig. It's not a meaningful safety margin against the things people are actually worried about.
Claim: “I have a metal building, so I need closed cell.”
Reality: Almost never — see the metal building deep dive above. Open cell + OSB on lower walls performs better, costs less, and gives you a more workshop-functional interior. Our long-term commercial customers have made the switch and don't go back.
Claim: “Spray foam off-gases for years.”
Reality: False with modern, properly-installed product (both open and closed cell). Properly cured foam is odorless within 24 hours and meets current safety standards. The horror stories online are about jobs done with off-spec product or improper mix ratios — both avoidable with a qualified contractor.
Common Questions
Bottom line — which one should I get?
It depends on the application. Residential walls, attics, crawlspaces = open cell (Premier's default for almost all home work). Stem walls, below-grade exterior walls, underslab ductwork, cold-storage = closed cell. Metal buildings = open cell + OSB on the lower 8 feet (the math AND our repeat customers' experience both support this). Premier walks you through the right answer for your specific project during the free estimate — we install both products and recommend whichever fits the job.
Can I mix open cell and closed cell on the same building?
Absolutely. Common combo: closed cell on stem walls / below-grade portions + open cell on the above-grade walls and roof deck. Or open cell on the main building envelope + closed cell on a specific zone where its properties are needed. We design the combo around your specific structure during the bid.
If open cell is so much cheaper, why does anyone use closed cell?
Because it's the right answer for specific applications — stem walls, slab contact, cold storage, exposed shop walls where the foam stays as the finished surface. Closed cell earns its premium when its specific advantages genuinely matter. The mistake is defaulting to closed cell when an open cell job would have done the work for half the cost.
Is open cell safe for spray-foam-on-the-roof-deck applications?
Yes, and it's our default for residential attic conversions. Open cell is light enough to apply at full thickness on roof decks without overloading framing, has excellent thermal performance, and provides the air seal that makes the conditioned-attic strategy work. We've done many residential roof-deck spray foam jobs across the OKC metro using open cell and would happily walk you through references if you want to talk to past customers.
How do I know which product the contractor is actually spraying?
By touch, once it's cured — which only takes minutes. Open cell feels like firm bread or a dense sponge: soft, slightly springy, your finger sinks in noticeably when you press it. Closed cell feels almost like wood to the human hand: hard, dense, your finger barely makes an impression at all. The difference is unmistakable once you've felt both. (Most spray foam rigs — including Premier's — transfer the liquid chemistry from labeled manufacturer drums into onboard tanks before the work day, so you usually can't verify the labels at the jobsite. The post-cure feel test is the real verification.) Pricing is the other tell: closed cell costs roughly 2× open cell. If you're being billed for closed cell but the cured foam compresses easily under finger pressure, something's wrong — and any contractor who's evasive about which product they're spraying is a red flag.
Do you offer free estimates?
Yes — every estimate is free, written, and includes a clear recommendation of whether open cell, closed cell, or a combination is right for your project + why. We also walk you through the metal-building math directly if that's relevant to your job. Call (405) 659-1046 or fill out our contact form to schedule one.
“Professional, quick, easy insulation job and no mess too! Made such a difference in the summer heat and helped lower my electric bills. Thanks Premier Insulation!”
— Kim Caplinger