Fire resistance

PIR insulation, a thermoset material, stays intact during fire exposure by forming a protective char layer and remaining in place during the tunnel test (the tunnel test is the ASTM E84, “Standard Test Method for Surface Burning Characteristics of Building Materials,” which assesses the spread of flame on the sur­face of a material). Nevertheless, most PIR sheathing products can­not be left exposed and must be covered with an interior finish of a minimum V2" gypsum board or equivalent thermal barrier. Some manufacturers produce PIR panels with a 1.25-mil (up to 16.5 mil) embossed acrylic-coated aluminum sheet laminated to 1.0-mil alu­minum sheets on each side of the PIR core that are rated for inte­rior exposure. These panel types are used primarily in industrial and agricultural buildings but are also commonly installed on the interior of basement walls and may be left exposed.