What Is PIR Insulation? Plain-English Answers to Common Questions

Quick answer

PIR stands for polyisocyanurate. It is a rigid foam insulation, made in a factory and sold as boards with a facing on each side, usually foil. Its closed-cell core gives a low thermal conductivity (λ 0.022 W/mK on Kingspan TP10 and Recticel Eurothane GP datasheets), so a thin board gives a high R-value: 100mm at that λ gives R 4.50 m²K/W. This page answers the questions people ask most often. For the longer overview of benefits and installation, see our PIR insulation guide.

What does PIR stand for?

PIR is short for polyisocyanurate. Kingspan describes it as a thermoset plastic produced as a foam and bonded to a facing. "Thermoset" means that once it has cured it does not melt back into a liquid when heated, unlike a thermoplastic.

How is PIR insulation made?

According to Kingspan, the foam is cooked under pressure, cooled and cut into boards. The facings are bonded to the core during manufacture. For example, Kingspan TP10 has a low-emissivity composite foil on both sides, bonded to the core in the factory. Its core is a fibre-free, rigid thermoset PIR insulant.

How well does it insulate?

Insulation performance is measured by λ (lower is better) and R-value (higher is better). R equals the thickness in metres divided by λ. Datasheets round R-values down, which is why you see figures such as R 4.50 at 100mm and 2.25 at 50mm for a λ 0.022 board. To compare against other materials, see our PIR vs phenolic vs rockwool vs EPS guide. To see how much you need, read what thickness of PIR insulation do I need or use the PIR U-value calculator.

Where is PIR used?

• Flat roofs: boards such as Kingspan TR24 are designed for warm roof systems.
• Pitched roofs, framed walls and floors, which are the applications Recticel lists for Eurothane GP.
• Walls, as a core in insulated plasterboard, and in cavity walls as partial-fill boards. See our comparison of the main PIR brands.

Is PIR combustible?

PIR is an organic plastic foam, not a mineral product. The Kingspan TP10 and Recticel Eurothane GP datasheets declare Euroclass F, and TP10 points readers to the relevant technical bulletins for the route to compliance with the Building Regulations. If a project calls for a non-combustible product, a stone wool such as ROCKWOOL Flexi (Euroclass A1) is the sort of product that meets that description. Always check the datasheet for the exact board and the requirements of Approved Document B for the building.

Does PIR absorb water or rot?

Kingspan states that the TP10 core and facings resist mould and microbial growth and give no food value to vermin. The core also has a high resistance to water vapour (greater than 50 MNs/g for the core and greater than 100 MNs/g for the foil facing, per Kingspan's tests). It still needs a proper build-up around it, and condensation should be assessed to BS 5250 for each project.

How long does it last?

Kingspan says that, if correctly installed, TP10 will remain effective for the life of the building, and that its durability depends on the supporting structure and conditions of use. Installation is the part you control. See our guides to cutting PIR board and fixing and sealing PIR boards.

What can damage PIR?

Kingspan advises that the TP10 core is resistant to short-term contact with petrol, most dilute acids, alkalis and mineral oils, but not to some solvent-based adhesives, particularly those containing methyl ethyl ketone. Damaged boards, or boards that have been in contact with harsh solvents or acids, should not be used.

What affects the cost?

Thickness, brand, board size, quantity and delivery all play a part. We explain how to compare them in PIR insulation price per m².

Frequently asked questions

Is PIR the same as PUR?

They are related rigid foams, and the European standard BS EN 13165 covers factory-made rigid polyurethane foam products, which is why datasheets refer to PU. Check each product's datasheet for what is declared.

Is PIR insulation waterproof?

Do not treat it as a waterproofing layer. Kingspan describes resistance to mould and a high vapour resistance for TP10, but a roof or wall still needs its own weatherproofing and a condensation check.

How thick should PIR be?

It depends on the U-value you need and the build-up. Use the calculator, then check the manufacturer's tables.

Order PIR insulation

Browse our PIR insulation boards, including Eurothane GP 100mm. We have a £400 ex VAT minimum, with free delivery in England. British Gypsum (including Gypframe), Celotex and Knauf can also go to mainland Wales and mainland Scotland (£400 ex VAT minimum plus £40 + VAT delivery). Access panels can also go to mainland Wales and mainland Scotland, with their own charges (£15 + VAT under £300 ex VAT, free from £300). Other ranges, including suspended ceiling tiles and grid, are delivered in England only. We do not deliver to Northern Ireland or the Scottish islands. Call 03330 908479 if you would like help choosing.

Sources: Kingspan guide to types of insulation; Kingspan Thermapitch TP10 brochure; Recticel Eurothane GP product page; ROCKWOOL Flexi technical datasheet (Nov 2025). Figures are indicative and correct at the time of writing; they are not a substitute for a calculation by your designer or the manufacturer's technical team, and Building Control has the final say.