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."
[edit] Related articles on Designing Buildings
- Acrylic.
- An in-depth look at Environmental Product Declarations EPDs.
- Celotex RS5000 PIR insulation.
- Composites.
- ETFE.
- Fire behaviour of expanded polystyrene.
- Forever Chemicals.
- Glass reinforced plastic.
- Grenfell Tower fire.
- Insulation.
- LPCB certification and Kingspan.
- Loss Prevention Standard.
- Packaging.
- Plastic.
- Polyethylene.
- Polyurethane (PUR).
- Polystyrene.
- Persistent organic pollutants (POP)
- Phenolic foam insulation.
- Polyurethane spray foam in structurally insulated panels and composite structures..
- Sandwich panel.
- Specifying insulation for inverted roofs.
- Thermal insulation for buildings.
- Transparent insulation materials.
- Types of insulation.
- Types of plastic in construction.
- What do design professionals need to know about U-value calculation conventions?
Featured articles and news
We're expanding our collaborative mission by launching DB Intelligence, an exclusive market research advisory panel. Built environment professionals can now get paid to share their expertise on industry trends, products and services.
Panel members receive direct financial incentives for participating in research projects like short surveys, 1-2-1 interviews and focus groups. Register today to shape the future of the construction sector.
Planning condition discharge in England and Wales
A brief exoplanation from a building compliance expert, with further links.
Overheating guidance and tools for building designers
Guidance for dealing with element of building fabric control that have increasing importance.
Shading for housing, a design guide
From the Good Homes Alliance and British Blind and Shutter Association.
UK Standard Skills Classification (SSC)
A shared framework for describing skills needs.
Social media ban consultation comes to close
CIOB urges UK Government to consider social media’s role in careers guidance in ban debate.
The latest of eight Skills England apprenticeship units
The addition of battery manufacturing welcomed by ECA with a warning about the risks of fast-tracked apprenticeship units.
Building Control Independent Panel final report
A precis of a key report led by Dame Hackitt with full recommendations and link to the government response.
Building Safety recap April, 2026
A short and longer run-through of the month, with links to further information and sources.
CIAT May 2026 briefing.
From medieval scribes to modern word art.
ECA welcomes crackdown on late payment and push for clean energy, whilst CIOB seek fixed cladding removal timeframes.
Cyber Security in the Built Environment
Protecting projects, data, and digital assets: A CIOB Academy TIS.
Managing competence in the built environment
ITFG publishes new industry guide on how to meet the ICC principles.
The UK's campaign to reduce noise pollution: Mythbusting, articles and topic guides.