The thickest product manufactured by Celotex, XR4000, is a high performance, rigid polyisocyanurate (PIR) insulation board with low emissivity foil facings bonded to each side specifically designed for cut-to-fit applications. This board is made to provide a lower U-value in one single layer of insulation. This product uses a combination of blowing agents with low global warming potential and zero ozone depletion potential (zero ODP).

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XR4000 is available in size 2.4m by 1.2m with thicknesses ranging from 110mm to 200mm and a thermal conductivity of just 0.022W/mK. This product is lightweight and easy to cut, handle, and install.

It can be used throughout building projects to help maintain continuity of the insulation envelope and is suited to floor, wall, and roof applications. Specific applications include between ceiling rafter systems where a standard size insulation board such as the GA4000 range is not recommended.


  • Multiple Application Methods
  • Tapered edge
  • Can be used to improve the standards of the current building regulations.
  • Keeps energy bills low long term and maximises savings.
  • Creates a more energy efficient environment.
  • Can be applied to extensions, refurbishments, and new build projects.
  • Inbuilt vapour control layer
  • Thermal conductivity of PIR products does not change over time
  • Easy installation

Celotex is the only brand to manufacture an insulation board with two additional thicknesses above 150mm, designed for specific projects. The additional sizes in the XR4000 range are 165mm, and 200mm thicknesses. These unique sized boards cannot be found in other standard PIR insulation boards where boards generally range from 25mm to 150mm.

This board can be cut using a fine-toothed saw, this is accomplished by measuring the boards to size and making markings if necessary. Then placing the boards on a surface that allows the saw to go all the way through the board. A knife can also be used to score the board, then snapping the board over a straight edge, and then cutting the facing on the other side however given the thickness of the board the saw method is recommended. Any of cut of the insulation board should be kept in case of gaps within the installed insulation.

Protective clothing is recommended to prevent particles produced from cutting the insulation boards from causing irritation to the eyes or skin. Goggles, face masks, and gloves should be worn to provide protection

The Celotex packaging should not be considered as protection for the board against weather conditions. The insulation board should be stored on a flat surface in weatherproof conditions preferable inside a building. If the boards should have to be stored outside the correct weatherproofing materials should be provided. Boards that have been allowed to get wet should NOT be used.

Celotex PIR Insulation Board XR4000 can be installed in a range of methods. These methods include:

  • Ground floors – whether solid concrete, block and beam, or suspended timber joist, and including where underfloor heating is used.
  • Timber and steel-framed walls – between the studs.
  • Pitched roofs – between the rafters.
  • Flat roofs – in ventilated cold roof constructions, installed from inside the building.

To find out more about Celotex PIR Insulation Board sizes, see our guide below:

Reaction to Fire classification, according to BS EN 13501-1
Achieves a BRE Green Guide rating of A+. Certificate number ENP413
Environmental Management Systems – ISO14001:2015
All Celotex products are manufactured under Quality Management Standard – ISO 9001:2015
BBA Approved (Cert no 17/5405, 16/5352)
CE Marked (18.DOPXR4000-01) to BS EN 13165

More Information:
Available in sizes: 110mm, 120mm, 130mm, 140mm, 150mm, 165mm, 200mm
Product Code: XR4000
Thermal Conductivity: 0.022 W/mK
Material: Polyisocyanurate (PIR)
Dimensions: 2.4m x 1.2m

XR4000 Datasheet:

Stocked Thickness110mm120mm130mm140mm150mm165mm200mm
Lambda Value (W/mK.)0.0220.0220.0220.0220.0220.0220.022
R-Value (m2.k/W)5.05.455.906.356.807.509.05
Length (mm)2400240024002400240024002400
Width (mm)1200120012001200120012001200
Maximum Weight (kg/m2)4.544.935.325.716.106.698.06
Pieces per Pallet20201816161212

What are thicker insulation boards used for?

  • Thicker insulation boards such as the XR4000 range are often used when insulating deeper cavities. These applications include in between rafter applications in the ceiling., flat roofs floor insulation and solid wall insulation.
  • The XR4000 range provide a two in one product, as an alternative of having to double up with two or more layers of insulation materials to fill the cavity.
  • The thicker insulation board still provides a thermal conductivity of just 0.022W/mK. The one product achieves the same quality as using multiple boards.
  • By installing a thicker board instead of multiple thinner insulation boards, it can provide a much easier, quicker, and cost effective process of application.
  • Supplying your home with the correct insulation materials will provide a more energy-efficient and sustainable environment by helping towards the prevention of global warming and climate change. This will also save you money on your energy bills by keeping prevent heat from escaping your property.

How are XR4000 boards installed?

These boards are installed by matching the depth of the rafters to the thickness of the board.

  • Measure in between each individual rafter and cut the board to fit to size to that specific space as the spaces in between rafters may have different dimensions.
  • Slot the insulation board into the cavity so it fits tight and meets the back of the space. If the board is fit too tight, a fine-toothed saw can be run down each side of the board to allow room for the wood to expand.
  • Ensure the boards sit flush with no protrusions, a block can be used to pat the PIR board into place.
  • Another layer of thinner insulation material or plasterboard or a combination of the two can then be applied depending on what the space is.