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Celotex CW4000 Cavity Wall Insulation Boards

(3 Products)

As temperatures dip and energy prices soar, the need for insulation has never been greater. Celotex CW4000 Cavity Wall Insulation Boards are BBA Certified, polyisocyanurate (PIR) insulation boards designed to offer improved thermal performance in sealed cavity air spaces. Purposed solely for partial fill cavity wall applications, the boards boast a polyisocyanurate rigid foam insulation core flanked with a low emissivity foil facing; along with an exceptionally low thermal conductivity of 0.022 W/mK.

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Celotex CW4000 Cavity Wall Insulation Boards Applications 

CW4000 is an insulation board aimed specifically at partial fill cavity wall applications; this essentially means that there needs to be an air gap between the insulation and the external leaf.

Cavity wall insulation (CWI) is the process of filling the gaps (cavities) between external walls with an insulating material in order to combat heat loss. 

CW4000 cavity wall insulation board is manufactured to offer improved thermal insulation performance within cavity air spaces in both new and existing buildings.

For convenience's sake, the boards are sized specifically to fit the standard wall tie spacing requirements using cavity tie clips, reducing the overall thickness of insulation required to achieve the target U-value.

We stock CW4000 boards in thicknesses of 50mm-100mm - offering low U-values with thin solutions. 


  • Walls - External Wall Insulation - Partial Fill Masonry Cavity Walls

Please note - Celotex CW4000 is not suitable for use in external walls of buildings over 18 metres in height (England and Wales) or 11 metres in height (Scotland).

Changes in Building Regulations have restricted the use of combustible insulation in structures of the specified heights and above.

Celotex CW4000 Specifications

  • Excellent thermal performance with a thermal conductivity of 0.022 W/mK
  • Low emissivity foil facings - improving the achievable U-value
  • Conveniently sized boards for quick and easy installation between cavity wall ties
  • Zero ozone depletion potential (zero ODP) and low global warming potential (GWP)
  • Lightweight and rigid assisting with handling and fitting
  • Compressive strength: 120kPa

Celotex CW4000 Certifications

  • Euroclass F Reaction to Fire classification, according to BS EN 13501-1
  • Achieves a BRE Green Guide Rating of A - assists in demonstrating environmental performance in your BREEAM assessments
  • Surface spread of flame: Class 1
  • CE marking complying with BS EN 13165:2001
  • CFC/HCFC free

Frequently Asked Celotex CW4000 Questions

How Does Cavity Wall Insulation Work? 

CWI works by creating a barrier between the inside and outside of your property, which helps to keep heat in and cold out. Cavity wall insulation is designed to fill the space between two masonry cavity walls. They can even be friction fitted between joists and placed on flat surfaces that need to be filled. 

There are lots of different types of cavity insulation on the market from glass mineral slabs, and phenolic boards to PIR boards. These are available in both partial fill and full fill. 

What Is Partial Fill Cavity Insulation? 

Partial-fill insulation leaves a 25mm or 50mm gap between the insulation and the external leaf. Even if moisture makes it through to the outer leaf, there is very little chance that it will bridge through to the internal structure. 

Local authorities tend to require new build properties to have partial fill insulation inside masonry walls.

What Is The Difference Between CW Boards & CW Slabs? 

Cavity wall insulation boards, also known as insulation foam boards or rigid foam, are a PIR insulation solution created by sandwiching a rigid PIR foam between two aluminium facings. Out of all the thermal insulators on the market, PIR foam is one of the best; showcasing an impressive thermal conductivity of 0.022 W/mK.

Cavity wall insulation slabs, on the other hand, are most commonly made from glass mineral wool. These materials are usually made from at least a third of recycled materials. 

Insulation slab's flexibility allows them to fit around small variations in the wall construction, ensuring a snug fit around joints, and reducing the chance of thermal bridging. 

How Effective Is Cavity Wall Insulation in Improving Heat Retention? 

Given that walls are to blame for approximately a third of heat loss in uninsulated buildings, installing cavity wall insulation is a no-brainer for those wanting to radically decrease heat loss and energy bills. 

On top of improving heat retention, cavity wall insulation is also one of the cheapest energy-saving measures you can install. What's more energy saving results in a lower carbon footprint - a welcome bonus for the green-minded amongst you. 

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