Can Insulation Catch Fire? Flammability Of Fiberglass, Spray Foam, Cellulose, Rockwool & Styrofoam

Insulation materials are created to stop as much heat loss as possible. These materials are typically made up of different components and have distinct properties. A frequently asked question regarding insulation materials is whether they can catch fire or not.

Insulation can catch fire if subjected to high temperatures as in a house fire. Small and short fires like short circuits or a candle flame can’t get the insulation to burn since all of them are treated with fire-retardants.

Some insulation materials, like fiberglass, won’t normally catch fire but can even work as an accelerant in house fires. So this is more like, most insulations won’t catch fire but most of them will burn.

Therefore, when we observe whether insulation can catch fire or not, we have to consider the two situations; a normal fire, and a high-temperature fire.

Here is a quick table showing which insulation material can catch fire and which doesn’t;

Insulating MaterialFlammable?Safe in a house fire
Spray FoamYesNo
Can insulation burn

Before we deep dive into the details, let’s first see what the common reasons for a house fire are. They are;

  1. Short circuits
  2. Negligent smoking habits
  3. Lightning
  4. Chemicals and gases
  5. Fireplaces
  6. The heat from appliances and equipment
  7. Candles

Now, let’s discuss how each of these insulation materials behaves under different kinds of fire;

Can fiberglass insulation catch fire?

Fiberglass insulation is mostly made of glass fibers. Therefore, they have high heat resistance. You can put a candle flame or a torch on the insulation and it won’t be affected. So fiberglass insulation won’t catch fire from any of the common sources of house fires.

Why does fiberglass insulation won’t catch fire

Fiberglass’s primary component silica is a tough solid material that does not go down without a fight. After the inclusion of a few other ingredients, fiberglass is formed after being heated intensely. As far as the melting point of the finished product is concerned, fiberglass won’t break down unless inflicted with heat energy higher than 1,200 degrees Fahrenheit/650 degrees Celsius.  A small fire such as a short circuit around the fiberglass probably won’t even budge the material.

But what about a house fire?

Unfortunately, while fiberglass doesn’t catch fire normally (like from a match or a short circuit) that’s not the case in a house fire. In fact, fiberglass insulation can accelerate house fires. There are two problems with fiberglass insulation here;

  1. oxygen supply
  2. spreading of fire

Fiberglass insulation has air pockets in them which will act as a supplier of Oxygen, a gas that fuels the fire. This will intensify the fire and keep it burning longer than other insulations. In addition, fiberglass melts in house fires. A house fire temperature can exceed 1500 degrees Fahrenheit and the melting point of fiberglass is around 1200 Fahrenheit. The melted glass will keep the temperature high, and it will flow into other parts of the house causing more damage than if fiberglass insulation was not used.


Conclusion: Fiberglass is a good insulation material that won’t catch fire under normal circumstances. However, if the house is on fire, having fiberglass insulation will cause more damage.

Does Spray Foam catch fire

Spray foam is sort of a liquid froth that is generally made up of either Icynene or Polyurethane. It expands rapidly after making contact with a surface. Thanks to its fuzzy texture, spray foam can make its way into tight openings and small gaps. This makes the insulation material highly capable in terms of effectiveness. However, due to its exorbitant price and complex installation procedure, it is not always chosen by the average homeowner. Spray foam also does not come in the form of batts due to its composition. It needs to be blown in with the help of a blower. 

Now, the answer to whether spray foam is flammable or not heavily depends upon the type of foam you’re going for. Polyurethane spray foam insulation will catch fire immediately but Icynene spray foam will not thanks to the fire retardants included in it.

Furthermore, no components of icynene have the potential to ignite fire since they’re all inflammable. As a matter of fact, Icynene’s inflammability can handle a max of 30 minutes of a blazing house before it catches fire. 

Can cellulose insulation catch fire?

To be honest, cellulose is the safest insulation for a house when compared to other insulations except for Rockwool.

Cellulose insulation is made mostly out of recycled paper and mixed with fire retardants. You won’t find such an insulation material in the market with this many recycled components as its ingredients. In terms of cellulose’s composition, 85% of its overall ingredients consist of recycled paper while the rest is covered by borate and ammonium sulphate. Note that these two are fire retardants and are used to put out fires. Does that answer our question though?

Well, yes and no. Borate is responsible for the high fire safety ranking of cellulose, but there’s a catch. Due to cellulose’s little combustibility rate, fires can start slightly easily but the flame would take a good while to spread through the material, thanks to the suppression by the fire retardant. In such a case, the fire would simply continue to seethe. This is both good news and bad news. Good news because the fire won’t spread easily and bad news because the smoldering fire in cellulose is very difficult to detect. The low melting point of cellulose is the reason for that.

In short; cellulose insulation can catch fire easier than other insulation materials but it prevents the spreading of fire, and hence cellulose insulation is safer than fiberglass or spray foam insulation in terms of fire hazards.

Don’t believe what I said? Given below is a video of a fire hazard test conducted between a fiberglass insulated, cellulose insulation, and a non-insulated structures. It took 25 more minutes for the cellulose insulated structure to collapse than the fiberglass insulated one.

Cellulose and fiberglass insulation fire test

The Flammability of Rockwool (Mineral wool)

Rockwool (Mineral wool) is made by bringing natural basalt rocks to their melting point under extreme heat conditions. At around 1,600 degrees Celsius, the rock melts and is mixed with a few other chemicals then spun at a high pace to achieve a material similar to thin wool fibers. Boasting extraordinary insulation capabilities, Rockwool or stone wool is then converted into batts and loose-fill to be used for insulation in homes, offices, and industrial buildings. Generally, Rockwool has the properties of fire resilience. It is often used solely for the purpose of fireproofing and it works like a charm.

This extraordinary ability to resist fire lies in rockwool’s tremendously high melting point which makes the chances of catching flame quite thin. Furthermore, even if Rockwool is exposed to extremely high temperatures, the material won’t emit any type of gas that may pose a threat to your loved ones. As a matter of fact, Rockwool is proven to delay the spread of fire due to its natural composition. This makes the insulation material one of the best when it comes to fire resilience. To conclude, rockwool insulation does not combust during contact with an average house fire. It’s going to take a lot more than just 1000 degrees Celsius to make Rockwool into ashes.

Don’t forget t watch the video below;

Is styrofoam flammable?

Styrofoam, also known as polystyrene used to be quite common back in the day for packing and wrapping. Even food used to be packed with this material. Styrofoam insulation, however, is still around to this day. It can put up a reliable barrier between an internal part of a structure and the external weather, which makes it a good material for insulation. Styrofoam’s composition consists of styrene, a product that is often identified as plastic. Due to its ingredients being widely available at a not-so-costly price, the material is the cheapest insulation solution you can get your hands on. Especially for spacious places where material needed for insulation is in large volumes.

Is Styrofoam flammable though? Due to its main ingredient polystyrene being derived from petroleum, Styrofoam is highly flammable. Regardless of its types, the primary element through which the material comes into being reacts instantly when it comes into contact with high temperatures. This is why Styrofoam is considered to be one of the most unsafe insulation materials out there. Its use and production are also limited in dozens of countries in the world because the material is highly dangerous to the environment in the long run. The non-biodegradable Styrofoam can take more than a thousand years to be fully decomposed. Therefore, using Styrofoam insulation or any polystyrene-based material in a place where a fire might get into is a terrible mistake.

Which is the most fire-resistant insulation?

Here is a video showing the flammability of fiberglass, rigid board, spray foam, and rockwool. As expected, Rockwool insulation is the most fire-resistant. See how the fiberglass accelerates fire at 13.30 minutes in the video; he says it is like Napalm!

The Importance of Examining Flammability in Insulation Materials

Now that you know everything that there is to know about common insulations and their ability to ward off fire, allow us to give you an insight into why this analysis is necessary. As mentioned previously, most people give little to no importance to an insulation product’s flammability whenever they’re planning to buy one. Although the main purpose of these materials is obviously not to save your house from a fire, they still play a great role in it. This is because fires spread significantly faster in this age as compared to the 20th century. The reason? Increased use of chemicals and materials. 

Studies have shown that a house fire can double within a span of just 30 seconds. Therefore, every second counts when it comes to escaping from a house that is caught in flames. Smoke is the most common reason behind deaths by house fires. It’s extremely important to know which insulation materials may help the spread of smoke or fire. Since fire thrives on oxygen, some materials such as fiberglass would help it spread in case the material is melted. This happens because when fiberglass is decomposed, it releases oxygen into the air. Even though the material itself is fireproof, it can heavily contribute to the spread of fire.

Tips to Minimize Fire Risks

There are several ways of ensuring that your insulation does not contribute to a house fire. Take a look at the following safety tips that might save a valued life one day:

Adhere to Legal Residential Codes

Abiding by the laws of your state and building is necessary for a reason. Whenever hunting for insulation material, be sure to examine its flame spread index. For example, the ideal insulation material should have a smoke development under 450 and a flame spread index that does not go beyond 25. These are Michigan’s residential codes and you can look up the code of your own state.

Consult a Professional

Consulting a professional can never be a waste of time or money. Although the party you’re buying insulation from would probably give you a thorough insight into the material’s fire safety, there’s no harm in seeking help from other professionals as well. You can also get an idea of the basics such as how much insulation will be needed, installation procedure, etc.

Sneak a Peek at Fire Ratings

The fire rating system helps determine how resistant a material is to fire. It also gives secondary information about how much smoke it emits or how fast will fire spread through it. Generally, fire ratings are divided into classes. Our area of interest lies in class A as insulation materials are included in this one. 

Prevention is Better

Statistical data has shown that insulation materials account for only 5% of total house fires. The cause lies not in the insulation, but in the kitchen appliances, gas cylinders, heaters, and electric boxes. Your best bet at minimizing the chances of a house fire is to keep an eye on all of these things and turn them off whenever they’re not in use. Insulation in rare cases can help the fire spread but if you can manage to prevent it from happening in the first place, the odds would be on your side. 

Charles John

Experienced HVAC technician with 8 years of experience in the industry. Capable of handling all sorts of heating and cooling equipment as well as proficient in operational management, construction-related techniques such as preventative maintenance, electrical troubleshooting and AutoCAD

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