PIR insulation board (cited as the FR5000 product of Celotex, a Saint-Gobain company) was proposed to be used externally in the refurbishment of Grenfell Tower, London, with vertical and horizontal runs of 100 mm and 150 mm thickness respectively; subsequently "Ipswich firm Celotex confirmed it provided insulation materials for the refurbishment." On 14 June 2017 the block of flats, within 15 minutes, was enveloped in flames from the fourth floor to the top 24th floor. The public inquiry into the fire determined that the Celotex cladding material was one of the primary causes of the rapid spread of the fire, as they were much more flammable then permitted by building regulations. Celotex deceived regulators about the fire performance of the cladding by secretly adding fire retardant materials to the cladding panels that were used during safety testing.