Flame Spread Index: 5
Smoke Developed Index: 35
Both figures place the material in Class A under both NFPA 101 (Life Safety Code) and the International Building Code — the highest classification available, and well below the thresholds for even Class B or C materials.
For context, the Flame Spread Index of 5 is extremely low (Red Oak, the reference material, scores 100), meaning the EPS core has a very limited tendency to propagate flame. The Smoke Developed Index of 35 is similarly minimal.
Interestingly, in a floor application, the EPS panel is fully encapsulated beneath the wood subfloor and finish flooring — it has no direct exposure in a fire scenario. And here’s the counterintuitive part: the other materials in a typical floor assembly actually perform worse on the same scale.
OSB and plywood radiant floor typically score in the Class B to C range (FSI 75–200), and wood finish flooring scores similarly. So the EPS is actually the best-performing material in the assembly from a fire standpoint — every layer above it is more flammable.
For residential construction, floor assemblies are also generally not required to carry a fire rating under the IBC or IRC, so there is no code-level concern here either.
To put things further in perspective: spray foam insulation — which is commonly used in wall cavities without much scrutiny — is tested under the same ASTM E84 standard and typically scores around FSI 25 and SDI 200–450. That’s significantly higher (worse) than our EPS on both flame spread and smoke development.
In fact, spray foam requires a mandatory thermal barrier (typically ½” drywall) under the IBC precisely because of those numbers.
Our EPS panel outperforms it on both metrics by a wide margin, yet is fully encapsulated in the floor assembly on top of that.