Celotex Isover

PIR Insulation

PIR insulation is the name given to polyisocyanurate insulation, a type of thermal insulation developed from polyurethane (PUR).

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The manufacturing process for PIR foam involves a chemical reaction, forming a closed-cell structure that traps a gas. This gas conducts less heat than still air resulting in one of the most thermally efficient insulation products available. This low thermal conductivity, combined with the material’s ease of handling and versatility in a wide range of applications has seen it become increasingly popular with building designers and contractors.

What is PIR insulation?

A variety of lightweight, rigid, plastic-based foam insulation boards are manufactured and sold as building insulation. Along with PIR there is also phenolic foam (PF), extruded polystyrene (XPS) and expanded polystyrene (EPS) plastic-based foam boards.

Plastic-based insulation materials can be categorised in terms of the type of plastic they are. PIR insulation is thermoset, meaning its manufactured state is its final state and any waste product cannot be melted and returned to the manufacturing process.

Manufacturing PIR insulation boards

Foam insulation like Celotex PIR comes off the production line in large sheets which are cut to the desired size. Once the chemical reaction is complete and the product allowed to cure, they can be sold and used for their intended application.

Generically, these different size products can all be described as ‘boards’. Smaller format products, like those designed for a masonry cavity wall, are often described as ‘batts’ or ‘cavity batts’ instead. ‘Batts’, however, has traditionally referred to glass mineral wool or stone mineral wool products also intended for cavity walls.

A ‘standard’ large-format board - usually 2.4m in length by 1.2m in width - is extremely versatile. For applications where a large area needs to be insulated, like a floor, boards can be easily laid in a staggered pattern covering the majority of the surface area quickly. Being easy to cut, a larger board can be divided to neatly finish off a row of boards.

What are other advantages of PIR insulation boards?

That easy cutting makes them a popular choice for pitched roof or framed wall constructions too. As accurately as rafters or stud frames might be built, there will always be some timbers at a slightly different distance to the rest, so cutting a larger board to the required dimensions will usually provide the best fit, the best installation and therefore the best performance.

PIR insulation often gives contractors and homeowners the best combination of affordability, availability and thermal performance in one material. Indeed, with the right equipment, experienced DIYers can safely handle and install the lightweight insulation.


Insulation products to consider
Product Name Thickness Range Sizes Lambda
Celotex Thermaclass Cavity Wall 21 90-140mm 1190x450mm (installed) 1205 x 465mm (including tongue) 0.021 W/m.K
Celotex CW4000 40-100mm Width 450mm, Length 1200mm 0.022 W/m.K
Celotex GA4000 50-100mm Width 1200mm, Length 2400mm 0.022 W/m.K
Celotex PL4000 25-65mm (+12.5mm Plasterboard) Width 1200mm, Length 2400mm 0.022 W/m.K
Celotex TB4000 20-40mm Width 1200mm, Length 2400mm 0.022 W/m.K
Celotex XR4000 110-200mm Width 1200mm, Length 2400mm 0.022 W/m.K