Is fiberglass considered combustible?

You see fiberglass used as insulation and assume it’s completely safe from fire. But reports of its performance in real fires are mixed, creating uncertainty for product specifications.

No, the glass fibers themselves are non-combustible. However, the resins and binders used to hold the fibers together are combustible. In a fire, these binders will burn, producing smoke and toxic fumes, even if the glass fibers themselves just melt.

This is a key detail many overlook. At our factory, we produce aluminum hydroxide, a mineral used to make products inherently non-combustible¹. We often talk with customers who are looking for safer alternatives to standard fiberglass²-reinforced plastics due to these fire safety³ concerns. The distinction between the non-burning glass and the burning resin that holds it together is the single most important factor when evaluating the fire safety of fiberglass products. Let’s dig into why this is so critical.

Is fiberglass a combustible material?

You need a clear yes or no answer for your safety data sheet. Ambiguous terms like "fire-retardant" are confusing and don’t provide the certainty you need for compliance.

Yes, fiberglass as a composite material is typically considered combustible because of its plastic resin content. While the glass provides strength, the resin acts as the fuel that can be ignited and burn.

To understand this, you have to see fiberglass for what it is: a composite material⁴. It has two main parts. First, the glass fibers, which are basically tiny strands of glass. Glass does not burn. It provides the strength and structure. Second, the polymer resin, which is a type of plastic like polyester or epoxy. This resin surrounds the fibers and holds them together in a solid shape. This plastic resin⁵ is almost always based on carbon, and it is a fuel. It will burn. The final product’s classification depends on the ratio of glass to resin and whether any fire retardants have been added. But without special treatment, the presence of that resin fuel makes the entire composite panel a combustible material. This is why a simple "fiberglass" label isn’t enough; you must know what the resin is and how it’s treated.

Will fiberglass burn in a fire?

You assume that even if it burns, it can’t be that bad if it’s used so widely. This assumption could lead to underestimating the real danger it poses in an emergency.

The glass fibers will not burn, but the resin binder absolutely will. This burning resin releases a great deal of heat and, more importantly, thick, toxic black smoke which is a major life-safety hazard.

In a real fire scenario, the heat and smoke are often more dangerous than the flames themselves. The resin used in fiberglass composites is a hydrocarbon fuel. When it burns, it undergoes combustion that creates a lot of soot and toxic gases like carbon monoxide. This is a significant problem. The intense smoke can quickly fill a space, making it impossible for people to see or breathe, blocking escape routes. For a professional like yourself, Mr. Park, evaluating a material’s contribution to smoke production⁶ is just as important as evaluating its flammability. This is a key advantage of mineral-filled composites. Our aluminum hydroxide doesn’t burn or create smoke. When heated, it releases water vapor, which is harmless and actually helps suppress the fire and dilute smoke. It’s a fundamentally safer reaction.

Does fiberglass melt or burn?

You need to know how the material will fail in a fire. Will it hold its shape or will it disappear? Understanding how it fails is key to designing safe systems.

It does both, in a specific order. First, the resin burns at a relatively low temperature. This releases smoke and fire. Then, at much higher temperatures, the remaining glass fibers will soften and melt, losing all structural integrity.

This two-stage failure process is a critical weakness. The burning happens first. A fire only needs to reach a few hundred degrees Celsius to ignite the resin. This is the stage that spreads flames and produces toxic smoke. As this happens, the material begins to lose its strength because the "glue" holding it together is being consumed by the fire. If the fire continues to grow and temperatures climb past 800°C (1470°F), the second stage begins: the glass fibers themselves start to melt. At this point, the material loses all its structural ability. A panel could warp, fall, or collapse, creating new openings for the fire to spread. This is very different from a non-combustible mineral board, which might crack under extreme heat but will not add fuel or disappear from the assembly.

What type of hazard is fiberglass?

You are focused on the fire risk, but you’ve heard workers mention other issues. To make a responsible decision, you must understand all the potential hazards associated with a material.

Fiberglass presents two distinct hazards. The first is a fire hazard from its combustible resin. The second is a significant health hazard from its sharp, microscopic fibers, which are a skin, eye, and respiratory irritant.

This is an extremely important point that goes beyond fire safety. In my experience, this health hazard⁷ is a major reason why many industries are looking for alternatives. When fiberglass is cut, drilled, or disturbed, it releases tiny, sharp glass fibers into the air. These can cause what’s known as "fiberglass itch⁸" on the skin and can be very harmful if inhaled, leading to serious respiratory issues. Because of these combined fire and health risks, many countries and regulators are putting much stricter rules on its use, especially for indoor applications or where workers are frequently exposed. We’ve seen a growing demand for mineral-based core materials and fire retardants precisely for this reason. A customer in your position, Mr. Park, can gain a competitive advantage by offering solutions that are not just fire-safe, but also safer for workers and occupants to be around.

Conclusion

Fiberglass is a combustible composite because its resin burns, creating toxic smoke. The material a dual threat of fire and health hazards, driving the market toward safer, mineral-based alternatives without these drawbacks.