FRP (fiber-reinforced polymer) is not inherently fire rated, but many FRP products are manufactured to meet specific fire ratings through the choice of resin, additives, and surface treatments. Standard FRP panels made with polyester resin will burn, but fire-rated versions can achieve a Class A flame spread rating, the highest classification for interior building materials. Whether a specific FRP product qualifies depends entirely on how it was made and what fire tests it has passed.
How FRP Fire Ratings Are Measured
The most common fire test for FRP wall and ceiling panels is ASTM E84, which measures two things: how fast flames spread across the material’s surface (Flame Spread Index) and how much smoke it produces (Smoke Development Index). Based on these results, materials fall into one of three classes:
- Class A: Flame Spread Index of 0 to 25, Smoke Development Index of 450 or less
- Class B: Flame Spread Index of 26 to 75, Smoke Development Index of 450 or less
- Class C: Flame Spread Index of 76 to 200, Smoke Development Index of 450 or less
Most building codes require Class A or Class B materials for commercial interiors, especially in healthcare facilities, commercial kitchens, and food processing plants where FRP panels are commonly used as wall coverings. When manufacturers label FRP panels as “fire rated,” they typically mean the product has been tested to ASTM E84 and achieved a Class A rating.
For FRP used in exterior wall assemblies, a separate and more demanding test applies. NFPA 285 evaluates how fire propagates through multi-story wall systems that contain combustible components. This full-scale test subjects an entire wall assembly to fire, not just a small sample, so passing it requires the FRP to perform well as part of a complete system including insulation and framing.
Why Resin Type Matters Most
FRP is a composite of glass fibers embedded in a plastic resin, and the resin is the component that burns. The type of resin determines the baseline fire performance before any additives are introduced.
Standard polyester resin, the most common and least expensive option, offers poor fire resistance on its own. When it burns, it decomposes almost completely, leaving only about 6% of its original mass as residue. That means nearly all the resin contributes fuel to the fire.
Phenolic resin performs dramatically better. In fire testing, phenolic FRP takes longer to ignite, releases less heat, and produces less smoke and fewer toxic byproducts compared to polyester FRP. When phenolic resin burns, roughly 55% of it converts to a carbonaceous char rather than combustible gas. This char layer acts as an insulating barrier, slowing the fire’s progress and allowing the material to retain some structural integrity longer. Phenolic FRP also maintains its load-bearing capacity at a slower rate of decline during fire exposure, partly because of this char formation and partly because of the resin’s thermal properties.
Vinyl ester and epoxy resins fall somewhere between polyester and phenolic in fire performance, though epoxy is more commonly used in structural FRP applications than in wall panels.
How Additives Improve Fire Performance
Most fire-rated FRP panels achieve their ratings through fire-retardant additives mixed into the resin during manufacturing. The most widely used additive is alumina trihydrate (ATH), a mineral filler that releases water when heated, cooling the material and diluting flammable gases.
Testing has shown that combining ATH with other strategies produces the best results. In one comparison, a standard brominated resin FRP panel scored a Flame Spread Index of 25 and a Smoke Development Index of 985. A panel made with ATH and an expandable graphite intumescent veil achieved a Flame Spread Index of 20 and a Smoke Development Index of just 125. That’s a massive reduction in smoke, which matters because smoke inhalation is the leading cause of fire deaths.
Other additives used in fire-rated FRP include ammonium polyphosphate, which reduces dripping and total flame time, and zinc borate. Manufacturers often use combinations of these to balance fire performance with mechanical strength, since high filler loads can make the material more brittle or harder to work with.
Structural Limits During a Fire
Even fire-rated FRP has a critical weakness: the resin softens at relatively low temperatures compared to steel or concrete. Every polymer resin has a glass transition temperature, the point where it shifts from rigid to rubbery. For most resins used in structural FRP, this temperature is below 100°C (212°F), well below the temperatures encountered in a building fire.
The practical consequences are significant. Research has shown that epoxy-based FRP can lose 73% of its strength at just 100°C. At roughly 100°C above the glass transition temperature, the material loses almost all load-bearing capacity. For structural FRP reinforcement bonded to concrete, the failure point isn’t the glass fibers breaking but the resin and adhesive softening until the bond fails. FRP reinforcing bars embedded in concrete become almost entirely ineffective once temperatures reach approximately 300°C (572°F).
This is why fire-rated FRP panels used as wall coverings in kitchens and bathrooms are a different conversation from FRP used as structural reinforcement. A Class A wall panel can resist surface flame spread effectively, giving occupants time to evacuate and limiting fire damage. But FRP should not be counted on to maintain structural strength during a sustained fire the way steel or concrete can.
Smoke and Toxicity Concerns
Fire ratings based on ASTM E84 account for smoke production, but they don’t directly measure the toxicity of that smoke. Research on epoxy FRP composites has found that these materials present a high fire hazard and can contribute significantly to fire growth. Carbon monoxide production is a particular concern, and the overall toxicity of FRP smoke, measured using fractional effective dose calculations, can be substantial.
Fire-rated FRP panels with proper additive packages produce far less smoke than standard versions. If you’re specifying FRP for a space where occupant safety is critical, the Smoke Development Index number is just as important as the Flame Spread Index. A product can technically pass Class A for flame spread while still producing problematic levels of smoke if it barely stays under the 450 SDI threshold.
What to Look for When Buying FRP
Not all FRP panels sold for wall applications carry a fire rating. Budget panels intended for garage workshops or agricultural buildings may have no ASTM E84 classification at all. When fire performance matters, look for these specifics on the product data sheet:
- ASTM E84 classification: Should state Class A or Class 1 (these are equivalent) with specific FSI and SDI numbers
- UL or third-party listing: Verified testing from an independent lab, not just a manufacturer claim
- NFPA 285 compliance: Required if the FRP will be part of an exterior wall assembly on a building over 40 feet tall, depending on your local code
Local building codes determine what rating you actually need. Commercial kitchens, hospitals, cleanrooms, and food processing facilities almost universally require Class A interior finishes. Residential applications may accept Class B or C, or may not require a rating at all. Your building inspector or architect can confirm the requirement for your specific project.