What is PIR insulation? A NZ guide

8 October 2026
Aaron Davis

PIR, short for polyisocyanurate, is a rigid foam insulation board. It's been common in Europe for decades and is now used more in New Zealand as the Building Code asks more of walls, roofs and floors. Here's what you need to know.

What it's made of

PIR foam forms when two liquids, a polyol and an isocyanate, react and expand. The foam sets hard into a closed-cell structure: millions of tiny sealed bubbles that trap gas and resist heat flow. Eurothane GP boards are then faced on both sides with a low-emissivity aluminium foil, which protects the foam and reflects radiant heat across an air gap.

The boards we supply are made by Recticel at its plant in Stoke-on-Trent, UK, in 2400 × 1200mm sheets.

How well it insulates

Insulation performance starts with thermal conductivity, measured in W/m·K. Lower is better. Eurothane GP's is 0.022 W/m·K.

For comparison, the highest-rated 90mm glass wool wall batt is R2.8, which works out at about 0.032 W/m·K. A 90mm Eurothane GP board is R4.05, around 45% more in the same thickness.

Thickness	R-value
25mm	R1.10
50mm	R2.25
75mm	R3.40
90mm	R4.05
120mm	R5.45
150mm	R6.80

The full range runs from 25mm to 150mm.

Where it's used

Walls: between the studs, over them as a continuous layer, or both. See our wall drawings.
Roofs and ceilings: between or under rafters, and especially in skillion roofs where depth is limited.
Floors: under timber floors, and under concrete slabs and screeds. It's compatible with hydronic and electric underfloor heating.
Special projects: tiny homes, vans, sleepouts, cool rooms and other places where every millimetre counts.

Other properties that matter on site

Moisture: after 24 hours fully immersed, water uptake is limited to around 2%, and the board keeps its shape when wet (FAQs).
Strength: compressive strength exceeds 140 kPa, so it can go under a slab or screed.
It won't sag or settle, so it keeps its thickness for the life of the building.
Cables: electrical cables can pass through without being wrapped; the board doesn't react with cable sheathing.
Environment: zero ozone depletion potential and a global warming potential below 5. The board rates A in the BRE Green Guide.
Fire: tested to BS 476 Part 7 (Class 1 surface spread of flame) and AS 2122.1 flame propagation. Test reports are on our Certificates page.
Warranty: 10 years.

The trade-offs

PIR costs more per square metre than glass wool batts, and it's rigid. Boards need to be cut accurately and the joints taped to perform at their best. A batt squashes to fill an uneven gap; a board doesn't.

That's why PIR earns its place where space is tight or where a continuous layer over the framing is needed. It's less compelling in an open ceiling space with plenty of depth for batts.

What it costs

Prices start at $80 including GST for a 25mm sheet (2.88 m²). A 90mm sheet is $225 including GST, or $67.93 per m² excluding GST. See the price list; quantity discounts may apply.

Want to know if PIR suits your project? Call us on 03 540 3003 or get in touch. We supply anywhere in NZ, with freight quoted on each order.