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Pilkington K Glass - Double Glazing, Replacement Windows - Pilkington K Glass, Low E Glass, Suncool Glass.

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What is the U Value of a typical Double Glazed sealed unit?

The following table shows some typical U values for vertical insulating glazing Pilkington Insulating Units and the effect of using K Glass, Argon and varying cavity widths. The lower the U Value - the better the insulator. U-value is the measurement of heat transfer through a given building material, glass, etc. In the UK all U Values are quoted as W/m²K.

Glass Specification Cavity Width
  12 mm 16 mm 20 mm
Optifloat/air/Optifloat 2.9 2.7 2.8
Optifloat/argon/Optifloat 2.7 2.6 2.6
Optifloat/air/Pilkington K Glass 1.9 1.7 1.8
Optifloat/argon/Pilkington K Glass 1.6 1.5 1.5
Overall width of Insulight Unit (mm) 20 24 28
Other Information:

U values based upon 4mm Pilkington Optifloat thickness. (NOTE: Optifloat is the name given by Pilkington to "normal" float glass)

Figures determined in accordance with the requirements of BS EN673: 1998 for `normal' exposure conditions. U values are rounded to the nearest 0.1W/m2K as described in clause 9 of the standard. The total overall U value of a window can be calculated taking into account the insulation of the glazing, the unit spacer and framing. 

We often get asked what is the best cavity width to use in a double glazed sealed unit. As can be seen above there is very little difference between a 16 mm and 20 mm cavity.

click here for a free brochure You will also note that adding Argon Gas alone has very little effect in improving the U Value. Only when the Argon is combined with Pilkington K Glass is any significant improvement made.


Pilkington are only one of many glass suppliers world-wide. We are only giving their products so much prominence here because of their large market share in the UK.
If you are from the USA you may well find this link of interest.
If you live in Australia we suggest you have a look at the Pilkington - Australia web site at
Different parts of the world quote U Values in different ways. In the UK all U Values are quoted as W/mēK. The lower the U Value - the better the insulator. U-value is the measurement of heat transfer through a given building material, glass, etc

Our contractors offer a wide range of glass options


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Coloured | Glass Extras | Introduction | Safety Glass | Pilkington K Glass | Patterned| Request Free Brochure | Values and Insulation | Warm-a-Glass™


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