Is Fiberglass Insulation Flammable? (No, Here's Why!)

Fiberglass is one variety of insulation that is made from fibers of glass, often with a polyester coating. The fiberglass may be used as a loose-fill or installed in batts, blankets or rolls. In blanket or roll form, it has a fairly unique fluffy look to it. This has drawn some concern to homeowners who think it might be flammable.

Fortunately, fiberglass insulation is not flammable. This is because it is made from glass and does not contain any hydrocarbons or vapors that can be oxidized to create heat and light. Because fiberglass does not create any heat itself, it is a much safer choice for filling the walls of your home. However, note that the paper or foil backings are the only parts that can actually catch on fire.

The material is also made purposely to be highly resistant to fire, as well as mold-resistant and pest-resistant. That being said, there are still some cautions to take when dealing with fiberglass in your home.

Fiberglass insulation comes in two forms: blanket and blow-in (commonly referred to as loose-fill). Both types of fiberglass insulation are created using molten glass, which is blown into fine fibers. Loose-fill requires special equipment and professionalism to perform, which is why blanket or roll is the most common type of fiberglass insulation for homes.

Fiberglass insulation is mostly made up of silica, which is an extremely hard, crystalline solid that can easily withstand high temperatures if it does not break down. Though it is usually white in color, fiberglass can be made to be any color of the rainbow.

Fiberglass insulation is also one of the most durable and cost-effective insulating solutions that can be found. It has an average cost around $0.64 to $1.19 per square foot. Because of its affordable cost and ease of installation, fiberglass is one of the most common types of blanket or roll insulation used in homes.

Since fiberglass insulation is, in fact, made of glass, it is not considered a flammable material and will not catch fire. However, it’s important to note that the paper and foil backings can catch fire. Fiberglass manufacturers will often add flame-retardant adhesives and foils to these backings to combat their combustibility.

Though, you can install your own flame-retardant product. FSK-shield is one such product, which also works as a vapor barrier. The product can be installed with the foil side exposed to help slow the speed of the flames as they spread.

While fiberglass insulation is not considered to be flammable, it can still burn or melt. This is because fiberglass insulation is made from glass fibers, and these fibers can emit toxic fumes when burned. When the fiberglass insulation reaches a high enough temperature, it can melt. Fiberglass insulation is rated to melt at roughly 1,400°F or 760 Celsius.

The most common area that fiberglass insulation will catch fire is typically around electronic devices such as heat exchangers. There have been numerous reports of fires in homes as a result of this. Fortunately, these fires are typically minor and easily controllable.

Another common example of fiberglass insulation melting or burning is if it’s exposed to any live electrical wires. These can create sparks or small fires that can be high enough temperatures to damage the condition of your insulation.

Or, if you have a chimney fire, which exceeds 1,700 degrees Fahrenheit, there is a chance that the fiberglass will melt. Then, the fiberglass may spread the heat to other materials that can ignite.

Because fiberglass insulation can still melt or burn, it can cause some serious problems if left unchecked. Based on its heat resistance, it isn’t likely that your blanket roll fiberglass will melt when exposed to fire. However, depending on the type of adhesive or its surroundings, temperatures can get hot enough to cause significant melting.

In these cases, melted fiberglass can increase the oxygen supply in your home. This can be a dangerous accelerant for all types of fires. Additionally, when fiberglass melts it can spread heat to other materials that might be more flammable, like wood sheathing.

Lastly, burned fiberglass insulation can send particles into the air, which can cause exposure to irritants like silica and boron. If you notice burned or melted fiberglass insulation, it’s recommended to remove it and properly install some replacement fiberglass insulation.

To better demonstrate these risks of melting, Dr. Energy Saver on YouTube has an excellent demonstration showing how fiberglass insulation reacts under extreme heat. You’ll see how fiberglass melts in the first minute:

While burning fiberglass insulation may not always result in a fire, it can diminish how useful it is. Insulation uses a scale known as an ‘R-Value’, which measures different materials’ thermal resistances. The higher the R-Value, the better a material is at insulating heat.

An insulation’s R-Value however isn’t a constant; it can be affected by temperature. Extreme changes in temperature can render some insulations less effective. Additionally, burning or melting fiberglass insulation will alter its thickness, which can dramatically lower its R-value.

For example, fiberglass batts and blankets have R-Values of about 3.3 per inch, 44% more effective than loose-fill fiberglass, which has an R-Value of 2.1 per inch. Depending on the severity of the burn, fiberglass batts clearly have the most potential for R-Value loss.

The most common type of irritant found in fiberglass is silica, which is a known human carcinogen. This can be very harmful to the lungs and can potentially cause conditions such as silicosis.

Because silica is so abundant in fiberglass insulation, direct exposure is considered a workplace hazard. A study by the American Lung Association found that 2.3 million workers in the United States are exposed to silica every year.