What Closed-Cell Spray Foam Actually Is

Closed-cell spray foam is a rigid polyurethane insulation created on-site by mixing two liquids — an isocyanate A-side and a resin B-side — that react on contact and expand roughly 30 to 40 times. The cured foam is about 2 lb/ft³, with 90%+ of its cells sealed shut and filled with a low-conductivity blowing agent rather than air. That sealed-cell structure is where every one of its properties comes from.

Here’s the part most articles skip. The R-value isn’t really coming from the plastic. Polyurethane itself is a mediocre insulator. What you’re actually insulating with is the gas trapped inside several billion tiny sealed bubbles — a blowing agent that conducts heat far worse than air does. Open-cell foam ruptures those bubbles on purpose and fills them with air, which is why it lands around R-3.7 per inch. Closed-cell keeps them intact. Same base chemistry, wildly different material.

That distinction explains everything downstream. Water can’t wick through a sealed cell, so closed-cell absorbs almost nothing — under 2% by volume. Air can’t pass through it either, which is why a single inch qualifies as an air barrier under ASTM E2178 while open-cell needs three and a half. Vapor diffuses through slowly, so an inch and a half turns the insulation into your vapor retarder. And because the cell walls are continuous and rigid, the finished foam has real compressive strength — around 35 psi in our own material, which is stiffer than a lot of people expect from something that started as a liquid.

How is it installed?

Two-component foam comes as an A-side and a B-side that never meet until the gun. On a professional rig, both sides are heated (typically 120–140°F) and pushed through a proportioner at high pressure — 1,000+ psi — into an impingement mix chamber where they collide, react, and leave the tip as a spray pattern. Cream time on our closed-cell is 2 to 3 seconds. Full rise, 12 to 16. You are not painting. You’re running a chemical reaction in mid-air and steering it onto a wall.

Passes go on in lifts of roughly 1.5 to 2 inches. That limit isn’t arbitrary — the reaction is exothermic, and a lift much thicker than 2 inches can trap enough heat in the core to scorch the foam. In bad cases it can actually smolder. Every applicator who’s been at this a while has either seen it or heard about it from someone who has.

Closed-Cell vs. Open-Cell: What Is Better?

Closed-cell is better where you need R-value per inch, water resistance, or structural stiffness in a shallow cavity. Open-cell is better where you need sound absorption, drying capacity, or the lowest cost per square foot in a deep cavity. Neither one wins outright — they’re two different materials that happen to come out of similar equipment.

The honest answer nobody in the industry likes giving: if you have unlimited cavity depth and no moisture concerns, open-cell often makes more financial sense. A 2×6 cavity filled with open-cell gets you roughly R-20 for about half the material cost of the closed-cell that would get you R-33. If you’re chasing a code number and you have the room, depth is cheaper than density.

Where that logic breaks down is in shallow assemblies, below grade, on the underside of a roof deck, on the interior of a metal building, in a van or trailer, anywhere flood exposure is real, and anywhere you need the insulation to also be your vapor control layer. Which, admittedly, is a lot of places.

Ranges reflect published values across major North American manufacturers. ArmorFoam-specific figures are in Section 17.

What Is the R-Value of Closed-Cell Spray Foam?

Closed-cell spray foam is generally rated between R-6.0 and R-7.0 per inch, with most current HFO-blown products landing near R-6.5 aged. ArmorFoam closed-cell tests at R-6.5 per inch aged by ASTM C518. Two inches gets you R-13. Three inches gets you R-19.5. Anyone quoting you R-7.5 or higher is quoting an initial value, not an aged one.

That aged-versus-initial thing deserves a real explanation, because it’s where a lot of marketing lives.

Why does spray foam lose R-value over time?

Fresh out of the gun, the cells are packed with blowing agent. Blowing agent conducts heat poorly, which is the whole point. But gas moves. Over months and years the blowing agent slowly diffuses out through the cell walls and atmospheric gases diffuse in — nitrogen, oxygen, carbon dioxide, all of which conduct heat better than what left. The R-value drops. The industry calls it thermal drift.

The curve is steep for the first several months, then it flattens out and essentially stops. Oak Ridge National Laboratory’s review of long-term thermal performance found that the five-year instantaneous value is roughly equal to the fifteen-year time-weighted average — which is why the five-year number became the standard stand-in for “what you’ll actually get.”

Two standards handle this: CAN/ULC-S770 and ASTM C1303. Both use thin-slicing to accelerate diffusion so a lab can predict a five-year value without waiting five years.

How much drift? Be skeptical of anyone who gives you a clean number. A Carlisle white paper cites an industry study where samples aged from 180 days to five years dropped 10% to 18%, averaging about 11%. Meanwhile ORNL’s 2023 blowing-agent assessment cites a study finding just 2.7% reduction over 3.5 years for one HFO formulation. The direction is clear — HFO-blown foams appear to age better than the HFC-blown products they replaced — but there’s no clean published head-to-head drift percentage for high-pressure closed-cell foam. We’re not going to invent one.

There’s a related point worth making about single-component canned foam, because it sits on the same search results as professional kits and it is not the same product. A canned “closed-cell” foam from a hardware store is a one-component moisture-cured urethane. It rates around R-5.7 per inch, cures by pulling humidity out of the air, and yields maybe 20 board feet per can. A two-component kit is a chemically balanced 1:1 reaction that rates R-6 to R-6.6 and yields 200 to 600 board feet. Both are technically closed-cell. They are not interchangeable, and the price per board foot isn’t remotely comparable.

Coverage & Cost Calculator

Spray foam is sold by the board foot — one square foot at one inch thick. Contractors quote by the square foot at a stated thickness. Those two units are the number-one source of confusion in spray foam quotes, and they are trivially easy to reconcile once you see the math. Enter your area and target thickness below.

What Closed-Cell Spray Foam Costs in 2026

Professionally installed closed-cell spray foam runs roughly $1.00 to $3.10 per board foot, or about $3.00 to $5.00 per square foot at typical thicknesses of 2 to 3 inches. DIY two-component kits land between $1.22 and $1.95 per board foot before you account for waste, PPE, or the fact that you’re not very good at this yet.

That last part isn’t a dig. Yield is a skill.

Here’s every major DIY kit on the market normalized to the only unit that lets you compare them. Nobody publishes this table, which is strange, because it’s the only way to tell whether a kit is a deal.

Kit prices are typical online retail as of August 2026 and move constantly. Rated yields are manufacturer figures at ideal conditions; real-world yield runs 10–25% lower.

Look at that last row for a second. A professional 55-gallon set yields around 5,000 board feet, which is why installed pricing can include labor, equipment, insurance, and margin and still land near what a homeowner pays for material alone in a kit. The Reddit consensus on this is blunt and basically correct: for anything above a few hundred square feet, the tanks cost nearly as much as hiring somebody who does this every day.

Where the money actually goes

• Material — usually 30–45% of an installed price. This is the part that scales linearly with thickness.
• Labor and mobilization — a crew, a rig, and a day. Small jobs carry a minimum charge because getting the truck there costs the same whether you spray 400 square feet or 4,000.
• Prep and masking — overspray goes everywhere. On a retrofit this can be a third of the on-site hours.
• Removal of existing insulation — pulling old batts or vacuuming blown cellulose out of an attic is its own line item, often $1–2 per square foot.
• Thermal or ignition barrier — drywall, or an approved intumescent coating. Frequently forgotten in comparison shopping. See Section 6.

Fire Code: Thermal Barriers and Ignition Barriers

All foam plastic insulation, including closed-cell spray foam, must be separated from the building interior by an approved thermal barrier — normally half-inch gypsum wallboard. In attics and crawl spaces meeting specific conditions, a lighter ignition barrier is allowed instead. A Class A fire rating on the foam does not exempt it from either requirement. This is the most misunderstood part of spray foam, and it’s the part that fails inspections.

We read every page currently ranking for this topic before writing ours. Not one of them mentions a thermal barrier. Which is remarkable, because this is the requirement that fails inspections and the one a homeowner is most likely to discover after the check clears. So let’s actually cover it.

Does spray foam need to be covered with drywall?

Usually, yes. IRC Section R316.4 requires foam plastic to be separated from the interior of a building by an approved thermal barrier: minimum half-inch gypsum wallboard, or a material tested and passing both the Temperature Transmission Fire Test and the Integrity Fire Test of NFPA 275.

You’ll hear the phrase “15-minute thermal barrier” constantly. Worth knowing: the current code text doesn’t actually say “15 minutes” — it points to NFPA 275. The fifteen-minute figure is the historical performance basis, and it means the barrier keeps the foam’s surface below a 250°F average rise for fifteen minutes while the exposed face follows the ASTM E119 time-temperature curve. Also note the benchmark is half-inch regular core gypsum, not Type X. The criterion is thermal, not a fire-resistance rating.

When can you leave spray foam exposed?

Attics and crawl spaces, under conditions. IRC R316.5.3 waives the thermal barrier in an attic when all of the following are true:

• Attic access is required by Section R807.1
• The space is entered only for repairs or maintenance — not for storage
• The foam is protected by an approved ignition barrier

The prescriptive ignition barrier options, verbatim from the code list, are: 1½” mineral fiber insulation · ¼” wood structural panels · ⅜” particleboard · ¼” hardboard · ⅜” gypsum board · corrosion-resistant steel at 0.016″ base metal thickness · and, for attics only, 1½” cellulose insulation.

IRC R316.5.4 does the same thing for crawl spaces — access required by R408.4, entry only for repairs or maintenance, same barrier list minus cellulose. That omission is real and people miss it.

How do intumescent coatings replace an ignition barrier?

Through IRC R316.6, the specific-approval path. Foam that doesn’t meet the prescriptive rules can be approved on the basis of large-scale fire testing — NFPA 286 with the acceptance criteria of R302.9.4, or FM 4880, UL 1040, or UL 1715. For spray foam specifically, the test protocol is ICC-ES AC377 Appendix X, a modified room-corner test that evaluates the foam and its coating together on walls and ceilings in one shot.

What comes out the other end is an evaluation report listing exact coatings at exact application rates. This is the concrete part, and it’s public. From BASF’s ESR-2642, for example:

Rates are from ICC-ES ESR-2642 and apply to that specific foam. They are not transferable between products. Always pull the ESR for the foam actually being installed.

Every no-ignition-barrier approval also carries the same conditions, which show up nearly word-for-word across evaluation reports: entry to the space is to service utilities and no storage is permitted; there are no interconnected attic or crawl space areas; air in the space isn’t circulated to other parts of the building; and required ventilation is provided.

That “no storage” condition matters more than people realize. Put boxes in a foamed attic that was approved under this path and you’ve technically left the conditions of the approval.

Climate Zones and Code-Minimum R-Values

The 2021 IECC requires R-30 ceilings in Climate Zone 1, R-49 in Zone 2, and R-60 in Zones 4 through 8. Wall requirements range from R-13 in the south to R-30 (or R-20 plus R-5 continuous) in the north. Separately, IRC R806.5 sets a minimum R-value of air-impermeable insulation that must go directly against the roof deck in an unvented attic — R-5 in Zone 1 rising to R-35 in Zone 8 — and that table is the one people miss.

Air leakage: the requirement people forget

Insulation R-value is only half the code. The 2021 IECC also caps whole-house air leakage by blower door test: 5.0 ACH50 in Climate Zones 1–2 and 3.0 ACH50 in Zones 3–8. The 2024 IECC tightened it further to 4.0 / 3.0 / 2.5 ACH50 and renumbered the section to R402.5.1.3.

This is where closed-cell foam quietly earns its price. An inch of it is an air barrier by test — ASTM E2178 air permeance under 0.02 L/s·m². Hitting 3.0 ACH50 with batts and caulk is achievable but takes real discipline from every trade on the job. Hitting it with a sprayed air barrier is close to automatic.

Does Closed-Cell Spray Foam Hide Leaks and Rot Roof Decks?

It doesn’t cause rot, but it does remove your early warning and it does slow drying. Building Science Corporation field-evaluated eleven in-service spray foam roof systems and found moisture contents within the safe range in every one, with no moisture damage. The single roof failure they reviewed traced back to foam sprayed onto wet OSB — an installation defect, not a design flaw. But the concern behind the question is legitimate and deserves a straight answer.

This is the loudest complaint about closed-cell foam anywhere online, and it usually arrives as a story. Somebody’s contractor found a joist bay that had been quietly holding toilet leak water for five years behind foam. Floor gone, joists gone. That story circulates because it’s real and because it’s the kind of failure that costs more than the insulation ever saved.

So here’s the accurate framing, which is more useful than either “foam rots roofs” or “that’s a myth.”

What actually happens to a leak under closed-cell foam

BSC’s research digest on unvented roof assemblies makes the mechanical point: rainwater migration is severely limited by the foam’s low water transmission and high adhesion, so damage stays local — confined to the area immediately around the hole. It doesn’t run down the sheathing and wet forty square feet. That’s genuinely good.

What you lose is the telltale. In a vented attic a roof leak announces itself as a stain on the sheathing or a drip on the insulation. Foam over the deck means the water is between the foam and the sheathing, where nobody sees it, and drying capacity in that spot has dropped substantially. The leak isn’t hidden by magic. You’ve just removed the inspection surface.

BSC modelled how much leakage different assemblies tolerate, expressed as a fraction of incident rainfall:

Building Science Corporation, BA-1312, Application of Spray Foam Insulation Under Plywood and OSB Roof Sheathing (Grin, Smegal & Lstiburek, 2013).

Read those numbers carefully, because they invert the popular narrative. Closed-cell dries more slowly but tolerates a larger leak volume. Open-cell dries faster but wets more. In the ORNL/ASHRAE sealed-attic field study in Charleston, physical water damage was observed along the rafters of the open-cell sealed attic — closed-cell showed the same trend with much less moisture transfer, because it’s less permeable to begin with.

Which produces the actual rule of thumb: never use spray foam as a band-aid over a wet or failing assembly. Fix the water first. That, not the material, is what went wrong in nearly every horror story.

Does spray foam cook shingles or void the warranty?

The temperature claim is much weaker than the internet thinks. The Florida Solar Energy Center measured this directly at their Flexible Roof Facility, comparing R-19 batts over a vented attic against six inches of foam at the roof plane. The difference in shingle temperature was a maximum of 9°F, averaging about 2°F across the day. Adding 9°F to a shingle already sitting near 150°F in July is not what determines its lifespan. UV is.

On warranties: we tried to find a single current, primary shingle manufacturer warranty document excluding spray foam, and we couldn’t. Secondary sources report Atlas requiring continuous airflow below the nailing surface and CertainTeed listing foam on roof decks as acceptable, but those trace to a contractor blog with a dead source link. So the honest position is that positions vary by manufacturer, the measured temperature effect is small, and you should read your specific warranty. Anybody claiming a blanket “spray foam voids all shingle warranties” can’t support it.

Vapor retarder classes, since this comes up constantly

Permeance by ASTM E96; class definitions per IRC R702.7.

ArmorFoam closed-cell tests at 0.83 perms at one inch, dropping to 0.10 at eight inches. That puts a nominal two-inch application solidly in Class II territory — which matters because IRC R806.5 requires exactly that in Climate Zones 5 through 8 for any air-impermeable insulation used in an unvented roof assembly. The foam satisfies its own requirement, at adequate thickness.

The UK Spray Foam Mortgage Story — And Whether It Matters Here

Roughly 250,000 UK homes have spray foam in the roof, much of it installed under government retrofit grants. By November 2024 a quarter of the UK’s largest mortgage lenders, and every equity-release lender surveyed, would decline a property with spray foam in the roof. The failure was overwhelmingly about installation, specification, and inspectability — not about closed-cell foam as a material. And the UK assembly type barely exists in American construction.

This shows up in American comment threads constantly, usually as “the UK is banning spray foam.” That’s not what happened, and the actual story is more useful than the rumor.

Much of the UK installation was driven by the Green Homes Grant, which covered up to two-thirds of the cost and closed in March 2022. In May 2025 the Property Care Association and HomeOwners Alliance published data from over 500 property inspections finding 35% of properties had one or more defect attributable to the spray foam installation. RICS had already released a consumer guide in March 2023 framing installation as a significant and fundamental alteration to a home, prompted by concerns about workmanship and high-pressure selling to vulnerable homeowners.

The lending problem followed from the survey problem. A lender needs a competent inspection of the roof structure. Foam sprayed directly onto the underside of tiles and battens makes that inspection impossible. So they declined.

What the government’s own modelling actually found

The Health and Safety Executive’s Building Safety Regulator published hygrothermal modelling of spray foam on timber sloped roofs in February 2024, predicting timber decay over five years. The results are more nuanced than either side wants:

HSE / Building Safety Regulator, Spray foam insulation applied to timber sloped roofs in dwellings: Modelling of moisture risk, February 2024. Risk bands: high >25% predicted decay, medium 1–25%, low <1%.

Read the pattern. Closed-cell modelled better than open-cell in most scenarios, because it is itself a vapour control layer. And risks were low across the board when the foam was applied per the prescriptive constructions in BS 5250:2021 — which require a vapour control layer on the warm side and a ventilated space between insulation and underlay. Where guidance wasn’t followed, things went badly. Sprayed straight onto tiles, everything failed.

Does any of this apply to US homes?

We searched for US equivalents and found nothing. No Fannie Mae, Freddie Mac, or FHA guidance treats spray foam as a lending defect. The only American content on the question is contractor marketing. Three structural differences explain why:

• Different assembly. The UK problem centers on retrofitting unvented foam into old tile-and-slate pitched roofs with high-resistance underlays and no vapour control layer. That assembly barely exists in US construction.
• We have a code for it. IRC R806.5 mandates the condensation-control R-value and requires a Class II vapor retarder in Zones 5–8 — exactly the control layer the failed UK installations lacked.
• Different market. The UK surge was subsidy-driven with weak installation standards and, per RICS, aggressive selling to vulnerable homeowners.

We could not find primary sourcing either way on how US insurers or appraisers treat spray foam. If somebody tells you they know, ask what they’re citing.

Termites, Pest Inspection, and Warranties

This is a real limitation and it is the one closed-cell foam’s supporters most often wave off. The issue isn’t that foam attracts termites. It’s that foam destroys the visual inspection that termite warranties are priced on — and in areas rated “very heavy” for termite probability, code prohibits foam plastic below grade on foundation walls entirely.

IRC R318.4 is the code section. In areas where the probability of termite infestation is “very heavy” per Figure R301.2(6), foam plastics shall not be installed on the exterior face or under interior or exterior foundation walls or slab foundations located below grade. Above grade, the clearance between foam plastic and exposed earth must be at least six inches. Exceptions exist for all-noncombustible or pressure-treated structures, for approved alternative termite protection methods, and for the interior side of basement walls.

States amend this. South Carolina requires a termite inspection gap of not less than six inches at the foundation wall and sill plate in crawl spaces. Georgia requires an inspection strip above and below the foundation wall exposing the sill plate and lower band joist.

Will spray foam void a termite warranty?

It can, and there’s a state regulatory document that says so plainly rather than a contractor opinion. The Georgia Structural Pest Control Commission issued SPCC Notice 18-04, “Spray Foam Insulation & Pest Management”, in June 2018. Its findings:

• Spray foam stops inspectors from fully performing inspections for wood-destroying organisms, and creates conditions that may invalidate a termite warranty
• Termites, carpenter ants, and rats can chew through spray foam, and the foam insulates those populations
• There are currently no inspection tools that overcome the visual obstruction — the Commission specifically doubted thermal imaging, moisture meters, acoustic emissions, and trained dogs as practical substitutes
• Pest management companies typically include contract language stating that products preventing visual inspection may negatively affect or void a warranty
• No scientific studies exist on fumigant interaction with foam, and there are no established post-fumigation re-entry times for foamed structures

Off-Gassing, PPE, and When You Can Move Back In

Twenty-four hours is the number most commonly cited for re-occupancy after professional spray foam installation — the CPSC recommends residents vacate for at least 24 hours, and most manufacturers say the same. The EPA explicitly declines to set a universal figure and points to the product’s own instructions. If the foam smells strongly days later, that’s not normal curing. That’s usually off-ratio material.

What is off-gassing, actually?

Somebody on Reddit asked this outright in a thread about closed-cell foam, and the fact that they had to ask says everything about how badly the industry explains it.

Spray foam is a 1:1 volumetric reaction. The A-side is isocyanate, usually MDI. The B-side is a polyol blend carrying catalysts, blowing agent, surfactant, and flame retardants, and it is the more complicated half of the equation by a wide margin. Meet at the right ratio, temperature, and pressure and essentially everything reacts and gets consumed. Miss, and unreacted components are left sitting in the foam with nowhere to go but into your air.

The smell people describe as fish, cat urine, or fresh latex paint is usually unreacted amine catalysts, per the Spray Foam Alliance. CPSC staff reached the same chemistry conclusion in a 2012 review: the odors identified after installation may not come from isocyanates at all, since those are highly reactive and get consumed — tertiary amines are more volatile, have lower boiling points, and carry strong ammonia-like odors. SPFA characterizes the odor as a nuisance rather than a chemical hazard and recommends supplementary ventilation for a few days.

The health question, answered directly

The exposure risk in spray foam is real and it belongs almost entirely to the applicator during installation, not to the occupant afterward. OSHA’s position: isocyanates are the leading attributable cause of work-related asthma, can cause sensitization, irritate eyes, nose, throat, and skin, and are classified as potential human carcinogens known to cause cancer in animals. The permissible exposure limit for MDI is 0.02 ppm (0.20 mg/m³).

That is why professional crews spray in full suits with supplied-air or organic-vapor respirators and why the building has to be vacated during and after application. It is also why “I’ll just do a whole attic with kits and a dust mask” is a genuinely bad plan.

What CDPH and GREENGUARD Gold actually certify

Both come up when homeowners get nervous, and both are narrower than people assume.

CDPH Standard Method v1.2 (the thing people call “Section 01350”) is a chamber emissions test. The product sits in an environmental chamber for 14 days, emissions are converted into modeled building concentrations for a standard classroom, private office, and single-family residence, and each product category must stay under half the California OEHHA Chronic Reference Exposure Level for each screened chemical — formaldehyde being the exception, capped at the full CREL of 9 µg/m³.

GREENGUARD Gold is built on UL 2818, screens more than 15,000 VOCs, and requires compliance with the CDPH method. UL doesn’t publish the numeric Gold limits, so we’re not going to print a number.

Racking Strength and Wind Uplift

Closed-cell spray foam measurably stiffens wall and roof assemblies. Testing commissioned by the spray foam industry showed racking loads roughly doubling to tripling depending on cladding and stud spacing, and University of Florida hurricane testing showed wind uplift resistance increasing 3 to 3.2 times with a full fill. None of it translates into engineered design capacity — no US model code lets you count foam as a shear-resisting element.

We’re going to be careful here, because this is an area where marketing runs well ahead of the data.

Compiled in Mason Knowles, The Use of Closed-Cell Spray Polyurethane Foam to Enhance the Structural Properties of Wall and Roof Assemblies, RCI/IIBEC, September 2010.

The fillet-versus-full-fill result is the genuinely interesting one and it rarely gets mentioned. Foam applied only at the sheathing-to-rafter joint — a fillet, not a fill — captured 1.9 to 2.2 times the original uplift capacity. That’s a large share of the benefit for a small fraction of the material. For a hurricane-region roof retrofit where you’re not trying to insulate, it’s a legitimately smart application.

The HFO Switch: Why Your Foam Changed

As of January 1, 2025, spray foam manufactured or imported in the United States must use a blowing agent with a global warming potential under 150. That ended HFC-245fa, which has a GWP of 1,030. Its replacement, HFO-1233zd(E), has a GWP somewhere between 1 and 4 depending on which reference table you use. Existing HFC-blown stock can be sold through January 1, 2028.

If you priced spray foam in 2023 and again in 2026 and the product name changed, this is why.

GWP values from the EPA Technology Transitions GWP Reference Table. Honeywell’s own datasheet for Solstice LBA lists GWP as 1 with a 26-day atmospheric lifetime; EPA’s regulatory table lists 4. Both are defensible depending on the assessment vintage — which is why we’re giving you a range instead of a single number.

The regulatory authority is the AIM Act, implemented through 40 CFR Part 84 Subpart B. The polyurethane foam subsector carries a GWP limit of 150 with a January 1, 2025 compliance date for manufacture and import. The American Chemistry Council’s Center for the Polyurethanes Industry confirms the 2028 sell-through date for existing HFC stock.

Did the switch make the foam worse?

No — if anything the opposite, though the data is thinner than you’d like. Oak Ridge National Laboratory’s 2023 assessment of HFOs as foam blowing agents measured low-pressure spray foam after 90 days of accelerated aging: HFC-245fa came in at 22.9 mW/m·K thermal conductivity, HFO-1233zd(E) at 21.2 — roughly 7% better for the HFO. Honeywell has reported yield improvements up to 10% and application in lifts up to 6½ inches versus the typical 2-inch lift for HFC versions, though that’s a manufacturer claim and should be read as one.

What the switch definitely changed is handling. Converting a rig from HFC to HFO isn’t a matter of swapping drums. B-side holding tanks, day tanks, and recirculating lines have to be completely drained, pump wet wells emptied and wiped. The two resins are incompatible and must not be intermixed. Any applicator who went through the transition remembers it.

One thing we’ll flag as unverified: you’ll hear that HFO foams need warmer substrate temperatures, often stated as a 60°F minimum. HFO-1233zd(E) does boil at 66°F versus about 59°F for HFC-245fa, which is the physical basis for the claim. But we couldn’t find that threshold in a primary manufacturer datasheet, so treat any specific temperature rule as product-specific until you read the TDS.

Can You Do Your Own Closed-Cell Spray Foam?

Yes, with a two-component disposable kit — and for small, bounded jobs it’s a reasonable choice. Rim joists, a van conversion, a shed, sealing a crawl space perimeter. Above roughly 500 square feet the economics collapse: kit material approaches the cost of hiring a crew, and yield gets worse the less experience you have.

The case for DIY is real for the right job. A kit is self-contained, needs no proportioner, and lets you spray twenty rim joist bays on a Saturday without scheduling a contractor for a half-day minimum charge. That’s a good use of a $389 kit.

The case against grows fast with square footage. Watch what happens:

DIY figures at $1.30/bf plus waste. Pro ranges from HomeGuide and InsulationRValues, 2025–2026.

Notice the bottom row. At whole-house scale a homeowner buying kits can pay more than a contractor charges — and the contractor’s price includes the crew, the rig, insurance, and a warranty.

If you’re going to DIY, the things that actually matter

• Chemical temperature, not just air temperature. Kit tanks want to be around 75–85°F. Cold chemical sprays badly, cures badly, and yields terribly. Bring the kit inside the day before.
• Substrate temperature matters too — generally 40–95°F, and it has to be dry. Foam on damp OSB is the documented cause of the one full roof failure Building Science Corporation reviewed.
• Respirator, not a dust mask. Organic vapor cartridges with a P95 or P100 pre-filter, plus goggles, chemical-resistant gloves, and a disposable coverall. OSHA’s permissible exposure limit for MDI is 0.02 ppm, and a paper dust mask does nothing about it. Not optional.
• Lifts of 1.5–2 inches maximum. Let each pass cool. Thicker lifts trap exothermic heat and can scorch the core.
• Once you crack the kit, you’re on a clock. Partial kits generally don’t store well. Plan to use the whole thing.
• Ventilate and stay out. Vacate for at least 24 hours per CPSC guidance and run ventilation.
• Remember the thermal barrier. A DIY attic or crawl space job still has to satisfy IRC R316.5 (or R303.5 in the 2024 IRC). Kits don’t come with an ignition barrier.

Where Closed-Cell Belongs — And Where It Doesn’t

How Closed-Cell Spray Foam Fails

Nearly every spray foam failure traces to one of six causes, and five of them are installation, not material. Knowing what they look like is the most practical thing on this page — it’s how you evaluate a finished job before you pay for it.

ArmorFoam Closed-Cell: Published Specifications

ArmorThane has manufactured polyurethane and polyurea systems since 1989, out of Springfield, Missouri, with a second facility in Edmonton. ArmorFoam closed-cell is our 2 lb medium-density system. These are the numbers off the technical data sheet, with the test method attached to each one — because a spec without a test method isn’t a spec.

Values from the ArmorFoam technical data sheet. Yield is theoretical at ideal conditions; plan real-world jobs at 10–25% less. Always pull the current TDS and SDS for the specific lot before specifying.

Frequently Asked Questions

References

Also see: Spray Foam R-Value Chart & Calculator · Open Cell Spray Foam Guide · ArmorFoam Closed Cell Product Page · Spray Foam Insulation Overview · Attic Foam Insulation · Crawl Space Encapsulation Guide