The Lowdown on PIR Insulation: Classification and Properties of Different Types


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The ever-evolving and constantly-changing nature of construction means that staying current with the best materials and techniques is often challenging. Most contractors consistently try to find the best tools and products at reasonable costs, hoping to satisfy customer demand and stay ahead of the competition.

Among those fundamental construction products are insulation solutions, especially PIR. Polyisocyanurate (PIR) insulation is a highly efficient material that can help keep homes and businesses warm in winter and cool in summer while reducing sound transmission within a building. With the latest technological advances and expert knowledge, it has slowly but surely, dipped its foot deep into the market.

How Thick Should PIR Insulation Be?

Generally speaking, a highly versatile 25 mm PIR insulation board should be enough to cover most needs. This includes a variety of applications, including solid floors, pitched roofs, and solid walls. The thickness of the board would depend on the type of property, its age and any existing insulation.

If you determine that 25 mm PIR insulation can’t cover your needs, there are 50mm, 75 mm or even 100 mm boards that would provide even more insulating properties, depending on the application. All thicknesses have low emissivity foil facings on either side that vastly improve thermal performance in sealed air spaces.

Classification and Properties of Different Types of Polyisocyanurate Insulation

Aside from the general range of thicknesses, several other factors determine the board’s overall performance and sustainability. While some options may offer improved thermal insulation, others could provide superior noise reduction or better compressive strength.

Density and Compressive Strength

This is probably the most influential factor in terms of the board’s ability to insulate and resist compression. The denser a board is, the better its performance will be on both counts. Density is usually measured in kg/m3, with the higher numbers representing greater densities.

It’s worth noting that most polyisocyanurate boards will offer compressive strength values at 10% deflection, usually ranging from between 100 kPa and 200 kPa. This is considered a high value and should be more than sufficient for general use.

Thermal Conductivity Ratings and R-Values

R-values are used to measure the board’s thermal resistance, which is how well it withstands the transmission of heat. Whenever it comes into contact with a heat source, higher-valued boards will be able to resist the damaging effects of thermal bridging. Some models even go as far as being completely fire-resistant, which is generally achieved through the use of fire retardant treatments.

The typical thermal conductivity for most polyisocyanurate boards ranges from about 0.022 W/mK for 25 mm boards to about 0.025 W/mK for 75 mm models. The way this value is expressed usually differs between manufacturers, so it’s important to clarify this point with your supplier before opting for a particular product.

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Noise Control and Durability

Naturally, when you place any kind of insulation on walls or floors, it should have some kind of soundproofing capabilities. On average, PIR boards should offer a noise reduction of up to 38 dB, which is usually more than enough to cope with the typical levels of sound within a home or office.

In terms of durability and longevity, polyisocyanurate is highly reliable and can last for decades without any serious signs of deterioration. This is largely due to its non-absorbent nature, which helps it resist moisture, UV radiation, and general wear and tear.

Brands to Consider

There are several manufacturers of these insulation boards that have been in the industry for many years and offer reliable solutions. Of course, the specific product you choose should be dependent on its properties and the application it’s intended for. Still, the consensus is that these four brands are amongst the best in terms of quality and performance:


With an impressive range of polyisocyanurate boards ranging from 25 mm to 100 mm in thickness, Ecotherm provides solutions for both wall and roof applications. Its products are known for their layered construction with several coatings of insulation, fire retardants, and vapour-permeable membranes.

The industry-leading compressive strength values (up to 300 kPa) and thermal conductivity ratings mean that Ecotherm’s boards are some of the most efficient on the market. The more sophisticated products also offer superior acoustic insulation and fire resistance.


Another recognised leader in the PIR industry, Kingspan is highly respected for the quality and performance of its products. Its Kooltherm range offers an impressive selection of boards with numerous performance-enhancing features, such as high compressive strength ratings, excellent thermal insulation, and exceptional noise reduction capabilities.

Their core water-resistant foams ensure that the boards can be used in both wet and dry areas without suffering any deterioration. When combined with their vapour-sensitive membranes, they provide a more comprehensive solution to moisture infiltration.


When it comes to getting solid value for money, Mannok’s PIR boards won’t let you down. Their foil-facing technology offers exceptional acoustic insulation, while their range of board thicknesses (from 25 mm to 100 mm) provides flexibility in terms of application and performance.

When you combine this with their fire-resistant treatments and water-repellent membranes, you get a board that’s suitable for both internal and external uses. And thanks to their competitive price points, you won’t have to break the bank when it comes to acquiring these products.

Quinn Therm

The composite foil facings of Quinn’s PIR boards make them some of the most energy-efficient solutions out there. This is because it helps to achieve a higher R-value than other comparable boards on the market due to the specific orientation of the foil layers.

What’s more, their impressive compressive strength (up to 200 kPa) and flexible facings have both flat and curved applications, with a degree of versatility that’s not easy to match. Regarding fire and water resistance, the board’s special formula ensures that it will keep performing at a high level for decades.

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How to Install PIR Insulation

Installing these boards is relatively straightforward and requires minimal technical knowledge to pull off. First, you’ll need to ensure that the space is prepped and ready – cleaned of debris and any other obstacles that might interfere with the adhesion of the boards.

Once you’ve done this, lay a thin layer of adhesive on the wall or ceiling and carefully attach the boards, making sure that they are flush with each other. From there, you’ll need to fix them in place with screws or nails and seal the seams with a specialised silicone-based mastic. 

And that’s it! Your PIR insulation is installed and ready to keep your home warm and comfortable.

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