Is Fiberglass Flammable Or Fire Resistant?

Fiberglass is a very commonly used material for construction in the modern day. It’s sometimes referred to as glass reinforced plastic or glass fiber reinforced plastic.

It is a lightweight and strong material that can be easily molded into a variety of shapes in ways that other, similar materials simply can not. That’s why it’s used in so many different applications and industries, including for bathtubs, aircraft, boats and home construction.

Is Fiberglass Flammable Or Fire Resistant

However, every constructor has to consider the potential risks and hazards associated with each material they use and consider whether it’s effective for its purpose, durable and fire resistant.

In the case of fiberglass, fire isn’t really an issue because it is fire resistant and will not catch fire, even in the extremest of heats.

In this article, we’ll be taking a closer look at what exactly fiberglass is, how it’s made and what makes it fire resistant.

What Is Fiberglass And How Is It Made?

Fiberglass is made from a substance called silica sand, which is mixed with limestone and soda ash. You’re probably already aware that glass is made from sand and it’s silica sand that is used for fiberglass.

The other two ingredients are incorporated into the recipe to lower its melting temperature and make it easier to construct.

Some brands use other materials and ingredients when constructing fiberglass to enhance it’s durability and make it even easier to produce.

The mixed ingredients are then heated to 2500°F and the molten liquid is then formed into fibers. These fibers can then be woven, flattened or randomly arranged into a sheet to be used for various purposes.

Inside the home, fiberglass is commonly used as insulation, in floors or walls, to keep heat inside the house and prevent cold air from seeping in.

What Does It Mean To Be Flammable?

A flammable substance is any one solid, liquid or gas that can ignite and burn when in air, if exposed to a source of ignition like an open flame or spark.

Flammable liquids all have a certain flashpoint, which is the temperature at which enough vapor is produced to ignite when exposed to an ignition source.

According to the University of Toronto, a liquid is classified as flammable if its flashpoint is below 37.8°C (100°F). Alternatively, a liquid with a higher flashpoint than this is known as combustible.

Fiberglass is a solid, until it is heated above roughly 1000°F, at which point it will melt and could potentially add more fuel to an existing fire. However, it is not flammable and so does not pose any risk of starting a fire in your home.

Liquid fiberglass can burn when exposed to temperatures as high as 1100°F, but at this point in a house fire, pretty much all substances are vulnerable to burning and there’s no real way to avoid it.

What Does It Mean To Be Fire Resistant?

A fire resistant material is one that will not fail when introduced to certain amounts of heat and will not allow fire to travel across it to other areas.

Fiberglass is a material that is designed to be fire resistant, meaning it will be able to resist heat up to a temperature of around 1000°F. This is what makes it excellent to use as insulation in walls, even in the event of a fire.

However, because fiberglass melts at this temperature, it is not a good idea to coat many things inside a house with it. A house fire can burn at temperatures up to 1500°F, at which point any fiberglass coated furnishings would be left with toxic, molten fiberglass coating it.

This can be extremely dangerous and harmful when coming into contact with skin and it can produce poisonous gases that are harmful to breathe in.

Is Fiberglass Dangerous In A House Fire?

Because fiberglass is fire resistant and non-flammable, it poses no danger of catching flame and causing a house fire. Under normal levels of heat, even a flame produced by a match, fiberglass insulation and other fiberglass home applications will not catch fire.

The only danger it poses is during a large-scale house fire, in which temperatures can reach as high as 1500°F. At this heat level, fiberglass will melt and will then be able to catch fire. If it does, it will produce toxic vapors that can be harmful to breathe in.

However, during a full-on house fire, there are many other substances in a house that will produce similarly harmful gases, so this shouldn’t be a main concern.

Also, once melted, it can be very harmful when in contact with human skin. Being burned by liquid fiberglass can be even more damaging than being burned by an open flame and is especially difficult to get off.

That’s why, during a house fire, it’s essential to stay away from any fiberglass insulation or other applications and evacuate as soon as possible.

Fiberglass Alternatives

Despite its non-flammability and fire resistance, some constructors opt to use alternative materials that can be even safer.


The best alternative to fiberglass for use as insulation is cellulose, a material made from recycled newspapers.

Now, it may seem like newspaper is a counter-productive material to use when talking about fire resistance and flammability, but there are a few extra processes it goes through before it can be used in a house.

A chemical called boric acid is mixed with the shredded newspaper strips to act as a fire retardant. As well as making the substance safer against the dangers of fire, boric acid also helps to fight mold, wood decay and pests like termites and other insects.

There have been some controversial statements made about the safety of cellulose, claiming that it is a fire hazard compared to fiberglass.

However, it was later discovered that these claims were made by a manufacturer’s association that produces fiberglass insulation. Talk about drama in the construction world!

Why Is Cellulose Safer?

One of the biggest disadvantages to using fiberglass for insulation is that it contains some relatively large pockets of air. This allows fire to be able to travel through it more quickly and spread from one room to another through a wall.

Cellulose, on the other hand, is a much denser material with no pockets of air. This means there is much less space and oxygen for a fire to use to spread through walls from one room to another.

Of course, cellulose can not completely stop fire from spreading but it certainly slows the process down, making it a lot safer.

Why Don’t All Constructors Use Cellulose Over Fiberglass?

The main disadvantages of cellulose are its cost and ease of installation.

Roughly speaking, cellulose materials can cost around twice as much as similar fiberglass materials. This cost only includes the base material costs for each, however there are also costs of labor to be considered as well.

Specialist equipment needs to be used to install cellulose insulation and it takes a lot longer to carry out properly.

Final Thoughts

Hopefully, you now know a whole lot more about fiberglass, its applications and its flammability.

In general, it’s a very safe and effective material to use in houses or any number of other construction applications.

While there is a safer alternative out there with cellulose, this material also has its downsides.

However, whichever way you choose to go with your next construction, these materials won’t have you worrying about a fire breaking out.