U-values measure how effective a material is at insulating. The lower the U-value reading, the better the material is at insulating heat.


U-values are used as a guide to insulation and performance of a material, as well as showing how effective it is at reducing the transfer of heat. U-values are commonly used throughout the building industry with contractors regularly specifying minimum requirements.

Storm’s bespoke secondary glazing has been tested and proven to achieve a U-value of 1.8 W/m²K. Please contact us for a copy of our independent test results.

Our bespoke secondary glazing system is able to achieve good insulation values as it utilises the cavity space between the primary and secondary units to act as an insulator. Using glass rather than acrylic also helps when used with our magnetic system – our rubberised magnetic seal acts as a thermal break preventing cold bridging.

To achieve the optimum insulation values we offer low-emissivity glass ('K' glass) which has an invisible coating to dramatically reduce heat transfer and reflect interior heat back into your room. This allows us to achieve our maximum value of 1.8 W/m²K.

Please refer to the following data sheet from Pilkington showing the general performance of Pilkington 'K' glass and the U-value.



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James Scott Road, Halesowen, West Midlands, B63 2QT
Telephone: 01384 63 63 65 Fax: 01384 41 03 07 sales@stormwindows.co.uk
VAT: 113 4319 53 Company Reg: 4076633

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