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Celotex  |  SKU: CW4100

100mm Celotex CW4100 Cavity Insulation - 1200mm x 450mm - 6 Boards

£47.79 Ex VAT
£57.35 Inc VAT
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Thickness: 100mm
50mm
75mm
100mm

This Celotex CW4100 is a partial fill insulation for masonry cavity walls. It is a high-performance rigid polyisocyanurate (PIR) material which is available in 100mm thickness and has been pre-sized so it can fit between cavity wall ties. It's a versatile option suitable for use in both new and existing builds as well as extensions.

CW4100 insulation has excellent thermal conductivity value of 0.022 W/mK, and the innovative low emissive aluminium foil facing helps it to achieve impressive uValues. As a result, it's among the best-performing insulation materials available on the market, bringing you reliable long-term savings.

  • Quick & easy to install
  • High-performance partial fill PIR insulation board
  • Low emissivity foil facings
  • Improves thermal insulation performance in cavity air spaces
  • Suitable for masonry cavity walls
  • CS(10\Y)120 compressive strength (kPa)

Celotex CW4100 insulation board has been specifically sized to fit the standard wall tie spacing requirements. This means that no cutting is required, making it quick and easy to be installed. When fitted correctly, it will help you meet carbon dioxide emissions and energy use targets which have been set by the national building regulations.

Thickness: 100 mm
Length: 1200 mm
Width: 450 mm
No. Boards: 6
Coverage: 3.24 m²
R-value: 4.5 m²K/W
Thermal Conductivity: 0.022 W/mK
Maximum Weight: 3.65 kg/m² 
Certification: BA 16/5352 BBA  17/5405
Country Origin: UK


The R-value denotes the resistance to heat flow – the higher the R-value the more insulating the product is.

This sturdy PIR insulation comes with a BBA (British Board of Agrément) certificate and a BRE (Building Research Establishment) Green Guide Rating of A, which will help improve your environmental performance.

  • Thermal conductivity: 0.022 W/mK, according to BS EN 13165 for factory made rigid polyurethane foam (PU) product.
  • BRE Green Guide Rating: A.
  • Spread of flame: Euroclass F Reaction to Fire classification, according to BS EN 13501-1. Products with this level of classification are not provided with a rating for smoke emission.
  • Certification: BBA certified.

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  • Size
    1200mm x 450mm
  • Coverage (m²)
    3.24
  • Thickness
    50mm
  • Material
    PIR

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What is Celotex PIR Insulation Board?

Celotex is a brand of Polyisocyanurate (PIR) insulation board - a type of rigid foam insulation board backed with a foil layer, ideal for its exceptional thermal performance. It is a strong and light type of foam insulation board that keeps structures warm by trapping air inside. PIR insulation is lightweight, durable, and offers excellent fire resistance and thermal insulating properties, making it a super DIY-friendly solution that can easily be cut to size to fit rafters, joists and stud walls, and used as Cavity Wall Insulation. We also sell a Celotex PIR Insulated Plasterboard which is ideal to save time in stud wall applications. 

How to Install Celotex Insulation Board

Due to it’s versatile nature, there are many different uses for PIR Insulation and therefore many different ways to correctly install it. However, generally PIR insulation should be purchased to fit the depth of the cavity or space it is to fill. It can be cut to size to fit the height and width of cavities, joists and rafters using a sharp utility knife or handsaw for thicker boards. It is typically designed to be friction-fit to a space, meaning the boards should fit tightly and stay easily in place with no additional fixtures and fittings.

For precise installation instructions for your specific use case, it is recommended to consult your builder, architect or building inspector to ensure installation complies with building regulations. 

Celotex vs Recticel

Celotex and Recticel are both brands of foil-faced PIR Insulation board available in a range of thicknesses. They are comparable products made from similar materials and methods and from a construction perspective they have the same Fire Rating (Euroclass F Reaction to Fire classification, according to BS EN 13501-1)  and thermal conductivity value of 0.022 W/m.K and so are suitable for largely the same purposes and projects. 

Celotex U-Value Calculator

Use the Celotex U-Value Calculator to help calculate the correct u-value of your project to ensure it complies to all of the required building regulations.

Thickness: 100mm
50mm
75mm
100mm