100mm PIR insulation board (cited as the RS5000 product of Celotex, a Saint-Gobain company) was proposed as the columnar and horizontal external insulation to be used in the refurbishment of Grenfell Tower, London; 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 causes of the rapid spread of fire up the outside of the building have yet to be established. It should be noted that flames can occupy the cavity between the insulation material and the cladding, and be drawn upwards by convection, elongating to create secondary fires, and do so "regardless of the materials used to line the cavities".