Is Spray Foam Flammable?

I already talked about spray foam and its benefits in terms of heat and sound insulation (mostly soundproofing since that’s what this website is all about), but I haven’t really talked too much about a very serious issue that spray foam suffers from which is that it’s quite flammable.

In this article, I will be going over if spray foam is flammable, how flammable it is, the differences between fire resistant and fire retardant, how it compares to other materials typically used for sound- and heat insulation, and more.

So, without any further ado, let’s get started!

Difference between fire retardant and fireproof

There’s a lot of confusion surrounding this topic and both terms are often used as synonyms, but there is a clear difference between the two and it’s something you should understand when considering what materials to use for insulating your home:

Fire Resistant is defined as a material that is inherently resistant to catching fire (self-extinguishing) and does not melt or drip when exposed directly to extreme heat, while Fire Retardant is defined as a material that has been chemically treated to slow ignition as well as burning, and even to self-extinguish.

The biggest difference between flame resistant and flame retardant materials lies in how each is made, since without a special chemical application, a fabric will not qualify as flame retardant, while without being made of certain nonflammable fibers, a material will not quality as fire resistant.

To determine whether or not a material is Fire-Resistant it has to:

  • Self-extinguish in two seconds or less
  • Have a minimal length six inches or less if being used for arc flash protection, or four inches or less if being used for flash fire protection.

It’s worth noting that no material is 100% fireproof and that it’s just a matter of time and heat until it ignites, melts, etc., but the point of fire resistant and fire retardant materials is to give you time.

In the case of spray foam, it’s fire-retardant and not fire-resistant.

Is Spray Foam Flammable?

Spray foam can ignite and burn if exposed to a sufficient heat source and therefore is considered to be combustible and should be handled accordingly. In addition to being flammable, this kind of spray foam has chemical properties that produce smoke when ignited, which can render occupants of a house unconscious and even lead to temporary blindness.

Almost all spray foam insulation available for purchase contains, or should contain, flame retardant, because untreated foam is a fire accelerant.

Most of the foam insulation products coming to the market are either polyurethane or expanded polystyrene foam, both of which are manufactured from petroleum derivatives. Untreated and exposed to elevated temperatures or flame, these foam products will burn vigorously, producing high quantities of smoke, and spreading fire.

The benefit of spray foam, however, is how easy it is to use and how well it performs in terms of heat- and sound insulation, but it’s definitely not as good for preventing fires as something like rockwool which can withstand temperatures of over 1.000°C, similar to fiberglass which won’t burn as well.

You can check this video where spray foam, as well as other insulation materials, are set on fire and you’ll see how the spray foam seems just slightly burn… until it doesn’t.

Testing The Burn Ability Of Insulation In Wall

Is canned spray foam flammable?

Canned spray foam is quite flammable when released from the can due to the use of a potentially explosive gas propellant which forces the product out of the can. As soon as it’s out of the can, the foam will immediately begin to cure, and depending on the type of foam (if it’s got flame retardant or not) it will be highly flammable or not so much.

All spray foam insulation is flammable, even the ones marketed as not, and it should always be treated as such.

Is uncured spray foam flammable? What about cured spray foam?

Cured spray foam is the one that’s had time to harden, and it’s also the one I referred to in the beginning as being quite flammable.

Uncured spray foam is just as flammable, but just like it happens with canned spray foam, the gas propellant used to push it out is very flammable and is heavier than air, which sinks and forms an invisible cloud which could burst into flames, or even explode, if an ignition source is present.

Flame Spread Rating

The flame spread index is determined by the distance that a flame travels along a test substrate in a specific timeframe to determine its propensity to burn and how rapidly it can spread flames.

It’s divided into these 3 classes:

ClassFlame Spread Index
  1. Class A fire ratings indicate a flame spread rating between zero and 25. Materials that fall into Class A or Class 1 include; brick, gypsum wallboard, and fiber cement exterior materials. These materials do not burn well and are very unlikely to contribute fuel to a fire.
  2. With a Class B or Class 2 fire rating, the flame spread rating would fall between 26 and 75. This rating is typical for slower-burning whole wood materials, such as planks that are in the same form as they were when they were cut from the tree.
  3. A Class C or Class 3 fire rating has a flame spread rating between 76 and 200, which incorporates building materials like plywood, fiberboard, and hardboard siding panels, as well as any of the faster burning whole woods.

What is a good flame spread rating?

The lower the Flame Spread index the better, since this means that the flame won’t travel and spread as rapidly. Class A materials, which have a rating of 0-25, do not burn well and are very unlikely to contribute fuel to a fire, which makes them the safest ones.

Spay foam compared to other insulation materials

Here’s a quick table with the Flame Spread rating, smoke development and STC (Sound Transmission Class) of the most common insulation materials (Spray foam, rockwool, fiberglass, Cellulose, MLV).

Note: As far as the STC rating goes, it refers to what type of insulation material works best when put inside a typical interior wall with ½” of drywall on either side, which has an STC rating of 34 on its own, and how it increases this rating.

MaterialFlame Spread RatingSmoke DevelopmentSound Transmission Class
Spray Foam7545039 for open cell 37 for closed cell
Mineral Wool (Rockwool)255045
Mass Loaded Vinyl2525033 

As you can see, out of all the typical insulation materials, spray foam is the most flammable. However, even though it’s flammable, it has a 1-hour fire rating, meaning that it will burn, but it will resist exposure to flame for one hour, giving people inside of the building enough time to get out.

Spray Foam Safety recommendations

  • Let a professional do the work, don’t apply the spray foam yourself.
  • Ventilate the room thoroughly to prevent propellant gas (methylene-diphenyl-diisocyanate 4,4) from building up inside the room, which may cause a fire or explosion.
  • Ensure that there are no naked flames, such as candles, gas cookers or gas fires in use while the foam is being applied and while curing.


Spray foam works really well for both heat and sound insulation, which is why many people use it for soundproofing, plus it’s really ease to apply since it will fill every nook and cranny much more easily than something like rockwool or fiberglass would.

The problem is that it’s quite flammable and that it also releases a toxic smoke than can be quite harmful to people.

If I were you, I’d stick to rockwool for all my soundproofing and insulation.


Is expanding foam a fire hazard? Spray foam insulation has a flame spread rating of 75, which means that it will spread fire to other combustibles fairly quickly. The propellant gas used to dispense of the foam (methylene-diphenyl-diisocyanate 4,4) is also highly flammable and could burst into flames if any ignition source is present.

Is spray foam insulation flammable after it dries? Cured spray foam can ignite and burn if a sufficiently high heat source is present and if given enough time, so it is considered flammable, even the one rated as fire-retardant, and it can spread fire to other combustibles with ease.

Last Updated on February 17, 2022 by Facundo

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