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Celotex CW4000

High performance PIR insulation for partial fill cavity wall applications.

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What is Celotex CW4000?

A partial fill insulation solution for masonry cavity walls, Celotex CW4000 is a rigid polyisocyanurate (PIR) insulation board with high thermal performance, suitable for use in new buildings and extensions. Sized to fit between cavity wall ties, it is lightweight and rigid; making it easy to handle, transport, and fit on site.

As well as being CE-marked, CW4000 is certified by the British Board of Agrément for cavity wall construction. Made at our original site in Hadleigh or our state-of-the-art facility in Eggborough (opened in 2018), you can be confident of it providing reliable, long-term energy savings that help to ‘future-proof’ your building.

How does CW4000 perform?

The entire thickness range offers a low thermal conductivity (lambda value) of 0.022 W/mK, putting CW4000 among the best-performing widely-available insulation materials on the market.

Celotex CW4000 will help to provide most of the thermal insulation performance in a cavity wall build up - but the overall heat loss from a building element depends on all of the materials used and the way they’re installed. Use our online and mobile U-value calculators to help you find the most efficient solution for your cavity wall.

Product benefits

The low emissivity aluminium foil facing on CW4000 helps to achieve lower U-values by increasing the thermal resistance of the air cavity it faces. Check our frequently asked questions for common queries about positioning and installing products correctly, or contact our technical services team.

Like all Celotex products, CW4000 is a thermal insulation solution that can help to meet energy use and carbon dioxide emissions targets set by national building regulations. 

  • Board size: 1200 x 450mm
  • Thickness : 40-100mm
  • Lambda: 0.022 W/mK
  • Facer: Low emissivity composite aluminium foil
  • Manufactured using a blowing agent with zero ozone depletion potential (ODP) and low global warming potential (GWP).


1With regard to partial fill cavity walls, the BBA certification assessed thermal performance, condensation risk, water resistance and durability.


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