Pure PET foam is combustible like most organic materials, but it is inherently halogen-free and produces less toxic smoke than some halogenated materials. For building applications, it is almost always used with fire-retardant (FR) additives or as a core within a non-combustible assembly (e.g., between gypsum boards or metal skins). FR-grade PET foam achieves good Euroclass ratings (e.g., B-s1,d0) and can meet stringent building codes when incorporated into a tested wall or roof assembly. It must never be left exposed.

