Fire Rated Spray Foam: Is Spray Foam Fireproof? Fire Ratings, Label Words and What They Mean
No. Spray foam is a combustible foam plastic, and no foam is hour-rated by itself. When a product is sold as fire rated spray foam, the label is describing one of several different things: how fast flame travels across its surface, whether it is part of a tested wall or ceiling assembly, or a small can of sealant that is not insulation at all. This page decodes the words so you can read a data sheet or a salesperson's claim. It does not replace the building official, who decides what your building needs.
What has to physically cover the foam, and the exceptions, are on thermal barrier and ignition barrier for spray foam. This page covers the rating terms only. PolyJacks sprays closed-cell foam only, inside buildings within about 35 miles of Spring Hill, KS.
Fire-proof or not: the plain answer
Three facts carry the answer.
- The foam burns. The Department of Energy's Building America guide says both open-cell and closed-cell foam are combustible, and are formulated with fire retardants and other additives to reduce flame spread and smoke (DOE Building America, Which Spray Foam Is Right For You?, 2009). A fire retardant slows the spread of flame; it does not make the material non-burning. That is the whole meaning of "fire retardant spray foam" and "fire resistant spray foam" on a spec sheet.
- Code treats it as combustible. Chapter 26 of the 2018 International Building Code requires foam plastic to be separated from the building interior by a thermal barrier, with listed exceptions (2603.4), and to carry the label of an approved agency (2603.2). The edition your office enforces may differ.
- Hour ratings belong to assemblies, not to a foam. More on that below.
The DOE guide is a federal document from 2009 and from another region. Combustibility is chemistry, so it holds in Kansas; the numbers on any current product come only from that product's own reports.
Fire rated spray foam: the label words, decoded
Read the table from the left. "What it tests" is the real subject; "what it does not mean" is the part sales language skips.
| Label word | What it tests | What it does not mean |
|---|---|---|
| Class A | A flame-spread index of 0 to 25 and a smoke-developed index of 0 to 450 in the ASTM E84 surface-burning test, which runs about ten minutes in a tunnel (USG Middle East blog, E84 and E119) | Not an hour rating, and not non-combustible. It ranks how a surface burns in one standard test |
| Flame spread index (FSI) and smoke-developed index (SDI) | The two numbers E84 produces. The code limit for foam plastic is a flame spread of 75 or less and a smoke-developed index of 450 or less when tested by E84 or UL 723 (IBC 2603.3) | A foam can be under the code ceiling and still burn. The guide above says the two foam types generally land under 25 and under 450, depending on thickness and formulation |
| "1 hour" or "2 hour" fire rated | Fire resistance by ASTM E119 or UL 263 (IBC 703.2), which the USG source describes as evaluating whole assemblies, reported as time such as one hour or two hours | No spray foam carries an hour rating as a product. A listed assembly number does |
| Thermal barrier | A covering such as 1/2-inch gypsum board, or a material that passes both the Temperature Transmission Fire Test and the Integrity Fire Test of NFPA 275 (IBC 2603.4) | A layer over the foam. It is not a property of the foam |
| NFPA 286, FM 4880, UL 1040, UL 1715 | Large-scale tests the code names when foam is specifically approved without a thermal barrier (IBC 2603.9) | An approval for the tested foam, thickness and assembly only |
| Listed, or an evaluation report (ESR) | The foam's maker had a third party evaluate it for stated uses, which the code expects to show on the package label (IBC 2603.2) | A blanket pass. The report lists the uses; anything outside them is not covered |
| Fire block | A small-can sealant for gaps and penetrations. See the last section | Not wall or attic insulation |
Two points the table cannot hold.
First, Class A is a narrow band; the code ceiling is wider. The E84 Class A range stops at an index of 25. The code ceiling for foam plastic is 75. A product that passes the code without being Class A is possible, and a Class A product still has to be covered or specifically approved. Do not let the letter stand in for the rule.
Second, E84 is a surface test on a standard sample. It reads how flame moves across the foam's face in a tunnel. It tells you nothing about how long a wall stays up in a fire.
Hour ratings belong to assemblies
A fire-resistance rating answers a different question from E84: how long does a wall, floor or roof assembly keep a fire contained and stay in one piece? Under the 2018 IBC, section 703.2 sets the ASTM E119 or UL 263 test procedures, and section 703.3 lists other ways to establish a rating, such as designs from approved sources, prescriptive designs, calculations or an engineering analysis of tested designs.
Every one of those routes rates an assembly: framing, sheathing, insulation, the board or panel on each side, the fasteners. Change one layer and the rating does not follow. This is why "2 hour fire rated spray foam insulation" is not a property you can buy. What you can ask for is a listed assembly that includes a named foam at a stated thickness, with the listing number on paper.
For a steel building the practical consequence is this. If a wall or ceiling needs a fire-resistance rating, the rating comes from the assembly the designer or building official specifies, and the foam is one named layer inside it. If the wall needs no rating, the foam's rules are the barrier rules and the exterior wall requirements, on the barrier page above and on spray foam for metal buildings.
Questions to ask when someone says a foam is rated
- Rated for what? Surface burning (E84), hours (E119 or UL 263), or a large-scale approval (NFPA 286, UL 1715)?
- Which exact product, at what thickness? Reports are written for stated thicknesses and densities.
- Which assembly? An hour claim needs a listing number for the whole wall, ceiling or roof.
- Whose report is it? The maker's evaluation report or listing, not a sales sheet.
- Does the building official accept it for this building? Ask in writing, with the construction type and use stated.
Where foam is used in aircraft hangars and event barns the questions get sharper, because the use and the occupancy change what the code asks. The hangar case is on airplane hangar insulation, and the event-venue case on wedding barn and event venue insulation.
Fire block cans are a different product
A can labeled "fire block" is a gap-filling sealant, not insulation foam. One maker's data sheet describes its fire block product as a minimal-expansion polyurethane foam sealant that fills gaps up to 1 inch and is "specifically designed to impede the spread of fire and smoke through service penetrations." The same sheet lists the tests E84, a modified E814 and UL 1715 (Great Stuff Fireblock product sheet). E814 is a different standard from the E84 and E119 above. It is the through-penetration kind of test, which this page has not opened and does not describe further.
The DOE guide points the same way from the other side: for some ceiling penetrations a fire-stop rated foam may be required, and it can be sprayed first at those spots with the standard foam after (DOE Building America).
Three ways this causes trouble:
- Buying a can to "fire-proof" an insulated wall. The can is for small penetrations. It does not turn a spray-foam wall into a rated wall.
- Reading the can's claims onto the insulation. A "fire block" word on a sealant says nothing about the insulation foam beside it.
- Using the wrong one. The sheet above is for gaps and penetrations. It is not a tool for filling a cavity.
What PolyJacks does and does not say
We spray closed-cell foam in finished steel, post-frame and similar buildings. We do not design fire-rated assemblies, and we do not tell you that your building needs or does not need a barrier. The building official does. What a product's barrier listing and test reports must show is explained on the closed-cell spray foam page. No rating is claimed for our product here. Foam options in a steel building, including ones that do not use plastics, are compared on metal building insulation options compared.
FAQ
Is spray foam fire-proof?
No. Spray foam is a combustible foam plastic with no hour rating by itself. The code separates it from the room with a thermal barrier, or accepts a tested and listed assembly in its place. The building official decides which applies.
Is there fire rated spray foam insulation?
No foam is hour-rated by itself. Some foams are part of tested, listed assemblies, and some have large-scale test approvals for specific uses. The decoder table above shows which label word means which. The building official decides whether a listing fits your building.
What does a Class A fire rating on spray foam mean?
It means a flame-spread index of 25 or less and a smoke-developed index of 450 or less in the ASTM E84 surface-burning test. It does not mean the foam will not burn and it is not a fire-resistance rating in hours.
Is fire retardant spray foam the same as fire resistant spray foam?
Both phrases usually mean the foam has fire-retardant additives that slow flame spread. Neither phrase means it resists fire for a period. A period is an assembly rating in hours.
Book a free on-site measurement
A fire question starts with the building. On the visit we record the wall and roof areas, the construction, how the space is used and who is inside it, and we flag anything the building official should see. You get a written estimate after the visit. The visit is free; how it works is on the free estimate visit.
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Pick "Spray foam insulation" on the booking form. We work within about 35 miles of Spring Hill, KS.
Spray foam insulation is a new PolyJacks service line run by its own crew and rig.
Who wrote this: PolyJacks spray foam team. Last updated: October 27, 2026. How it was made: drafted with AI assistance from the sources below, then checked against each source.
Sources
- International Code Council, 2018 International Building Code, Chapter 26 (2603.2, 2603.3, 2603.4, 2603.9), via the UpCodes Kansas viewer: up.codes
- International Code Council, 2018 International Building Code, Chapter 7 (703.2, 703.3), via the UpCodes Kansas viewer: up.codes
- DOE Building America / Consortium for Advanced Residential Buildings, Which Spray Foam Is Right For You? (2009): www1.eere.energy.gov
- USG Middle East, "Flame Spread Classification ASTM E84 and Fire Resistance ASTM E119" (a gypsum maker's blog, used for the plain-language split of the two tests): usgme.com
- Dow / DuPont, Great Stuff Fireblock Insulating Foam Sealant product sheet (a manufacturer's marketing sheet, used only for what that product says about itself): greatstuff.dupont.com
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