CavityTherm Flex is the perfect solution when insulating fair faced inner block walls or when block is laid flat resulting in an uneven surface to accept the insulation. The 20mm flexible fleece layer absorbs any variations due to block tolerances, providing a continuous unbroken bond between insulation layer and block. CavityTherm Flex achieves Passive level U-values as low as 0.14 W/m2K with excellent thermal bridging detailing in cavities less than 150mm wide.

  • Engineered HIPs facer provides wind driven rain protection
  • Moisture redirected to outer surface
  • Flexible backing to eliminate indentations
  • Prepositioned slots for sloping wall ties
  • Fully engineered jointing
  • Full range of accessory pieces build continuous system
  • Excellent Thermal bridging values
CavityTherm Flex U-values
(Inner block 215)
Block Type 125mm 150mm
Light 0.15 0.14 0.12
Med 0.33 0.16 0.14
Dense 1.15 0.17 0.14
Includes 5mm residual cavity, 20mm flexible fleece, plaster finish.
CavityTherm Flex U-values
(Inner block 100)
Block Type 125mm 150mm
Light 0.15 0.15 0.13
Med 0.33 0.17 0.14
Dense 1.15 0.17 0.14
Includes 5mm residual cavity, 20mm flexible fleece, plaster finish.
Property & Units
Water Vapour Resistivity >100 (MNs/gm)
Thermal Conductivity 0.021 (W/mk)
Service Temperature -20 to +100 (C)
CavityTherm Flex
Dimensions & R-values
Length (mm) 1200
Width (mm) 450
Thickness (mm) 125 150
Typical R-value* 5.50 6.70
* PIR and Flexible Fleece



The built-in full fill cavity wall insulation shall be CavityTherm Flex by Xtratherm,
including corner boards and ancillary detail components, comprising a rigid
Polyisocyanurate (PIR) core manufactured to EN 13165 between low emissivity foil
facings and Flexible Fleece to inner skin with engineered HIPS to outer skin. The
CavityTherm Flex _ _ _mm with a declared Lambda value of 0.021 W/mK (PIR) and
0.036 W/mK (Flexible Fleece) to achieve a U-Value of __ _ _W/m2K for the wall
element. To be installed in accordance with instructions issued by Xtratherm.
Refer to NBS clause F30 150, F30 12


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CavityTherm provides a ‘system’ that delivers on U-values, is practical, and with a full range of innovative detailing accessories – it delivers on continuity.

Learn More
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    Service Void Panels
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    Jointing Strip
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    Hockey Stick Insulation
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