Thermaclass Cavity Wall 21 (1190mm x 450mm) - All Sizes Insulation
Thermaclass Cavity Wall 21 (1190mm x 450mm) - All Sizes Insulation
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Thermaclass Cavity Wall 21 (1190mm x 450mm) - All Sizes


Est Delivery between and

This Product Is Sold In Pallet Quantities. Price Shown Is Per Pallet

Thickness Sheets Per Pallet Sheet Coverage Pallet Coverage
90mm 96 0.5355 m2 51.4 m2
115mm 80 0.5355 m2 42.8 m2
140mm 64 0.5355 m2 34.2 m2


Thermaclass Cavity Wall 21 is an easy to install, high thermal performance polyisocyanurate (PIR) insulation board for full fill cavity wall applications, with a thermal conductivity of 0.021 W/m.K. It can be installed with up to a 10mm residual cavity (to support ease of installation and accommodate mortar squeeze) or as a full fill solution with no residual cavity.

The boards have a low emissivity foil facing to each side and feature an engineered tongue and groove joint profile, helping to ensure a continuous layer of insulation to maximise thermal performance and provide protection from wind driven rain.

Product Features

  • Lightweight 1190 x 450mm boards (installed dimensions)
  • Tongue and groove edge profile
  • Low emissivity foil facing
  • BBA approved – certificate 16/5343


Product Properties

  • Board size: 1190 x 450mm (installed) 1205 x 465mm (including tongue)
  • Thickness : 90-140mm
  • Material: PIR


Product Performance

  • Lambda: 0.021 W/m.K
  • Reaction to Fire: Euroclass E Reaction to Fire classification, according to EN 13501-1 (Products with this level of classification are not provided with a rating for smoke emission)


Product Benefits

  • Excellent thermal performance with a thermal conductivity of 0.021 W/m.K, reducing the thickness of insulation required to hit the target U-value.
  • Low emissivity foil facing provides improved thermal performance in sealed cavity air spaces, improving the achievable U-value.
  • Easy to install – The boards are sized to fit standard cavity wall tie spacing. They are light and rigid, assisting with ease of transportation, handling and fitting.
  • BBA certified - Thermaclass Cavity Wall 21 has been assessed by the BBA as fit for use in defined full fill cavity wall applications if installed, used and maintained as set out in the certificate. 



  • External Walls – full fill cavity wall


Key Considerations

Thermaclass Cavity Wall 21 should not be used in the external walls of buildings over 18 metres in height (England and Wales) or 11 metres in height (Scotland). Recent changes to Building Regulations mean that only non-combustible insulation or insulation of limited combustibility can be used in buildings of that height.



Length 1190mm
Width 450mm
Thermal Conductivity 0.021 W/mK
BBA Approved Certificate 16/5343
Brand Celotex
Fire Rating Euroclass E
Material Type Polyisocyanurate

Est Delivery between and

Delivery will always take place on a weekday (Mon - Fri).
For information on delivery costs and more view our delivery info page.

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