Polyisocyanurate

Polyisocyanurate (PIR or Polyiso) foam insulation is known for its high thermal resistance as well as fire resistance compared to other foam insulants. Its behaviour under fire conditions has though recently come under great scrutiny since the role of Celotex RS5000 PIR insulation in the Grenfell tragedy in London UK in 2017. It has commonly for many years been used in commercial roofing systems, wall insulation, cladding systems in many modern buildings and as a component in structural insulated panels (SIPs). It ia also commonly used for industrial and commercial pipe insulation, laminated to aluminum foil and used for fabrication of pre-insulated duct that is used for heating, ventilation and air conditioning systems.

The core materials of PIR are similar to those used in polyurethane (PUR) except that the proportion of methylene diphenyl diisocyanate (MDI) is higher and a polyester-derived polyol is used in the reaction instead of a polyether polyol. The resulting chemical structure is significantly different, forming isocyanurate groups which the polyols link together, giving it a complex polymeric structure.

This structure means that PIR was generally accepted as performing significantly better than PUR against fire, previously thought to have excellent fire behaviour from being tested to high standards, the Grenfell tragedy bought much of this into question. Shortly after the fire on June 23 2017, the Police confirmed that small-scale fire tests had been carried out and Detective Superintendent Fiona McCormack commented "The insulation was more flammable than the cladding. Testss how the insulation samples combusted soon after the test started."

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