Pilkington K Glass Double Glazed Windows

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Ask an Expert - Pilkington K/Low E

Please note: Most of the answers we feature here are from 1999 - early 2002. We endeavour to keep all links etc up to date, however if you spot any errors please let our webmaster know at It should also be noted that some replies may change in light of changes to legislation especially with regards to Planning Permission and Building Regulations. To submit a new question or to query an existing question visit http://www.ask-questions.com/yabbse/index.php.

Question submitted by concerned

During a recent installation, I noticed that a patterned glass section sealed unit did not have K glass fitted (although it was specified at the time of order). I understood that the K coating was normally applied to the inside face of the inside pane. During discussions with the supplier, they stated that the K coating couldn't be applied to patterned glass (i.e. the inside pane). After further discussions, their suggestion is that the K coating will be applied to the inside face of the outside pane of (flat) glass, leaving the patterned glass as the inside pane (with the pattern on the inside of the sealed unit. Is the suggested change permissible? Is the K coating directional? Many thanks in advance for any advice.

This question answered by Tina Dunlop - The suggested change is permissible and is the best alternative as Pilkington K glass cannot be applied to textured (patterned glass).

It is correct that K Glass coating is normally applied to the inside pane of glass. However as its also normal for the pattern glass part of a sealed unit to be on the inside it will not be possible to have K glass fitted to the inside when patterned glass is specified.

We quote below from the Pilkington glass manual........

"In certain instances where a degree of privacy is required, Pilkington K glass may be incorporated as the outer pane of a Pilkington Insulating Unit, whilst incorporating Pilkington Texture Glass as the inner pane. The thermal insulation is the same regardless of whether Pilkington K Glass is positioned as the inner or outer pane. Any discernible difference in external appearance which may otherwise occur as a result of incorporating Pilkington K Glass as the outer pane will be nullified as a consequence of the Pilkington Texture Glass inner pane."

Question submitted by Tony

Is Pilkington K glass better or worse than Kappafloat glass.

This question answered by the Windows Today editorial team - Both of these types of glass have very similar properties. Basically Kappafloat was an "earlier" version of a low E type of glass by Pilkington. It was slightly more tinted than what we now know as Pilkington K Glass. Some people refer to Pilkington K Glass as Kappafloat - this may be what is happening here.

Question submitted by Stephen

I have a conservatory supposedly made with Pilkington K glass. I am unsure about this. How can I tell? 

This question answered by Tina Dunlop @ Almost Impartial Guide - The best way to tell is to use a coating detector. This is a unit which manufacturers and installers should have available. A detector costs about 60 and its quite easy to use. You simply press it against the glass with the "K" installed and from memory it either turns a red or green light on to confirm installation. A detector can usually be bought from specialist glass merchants or glass wholesalers. Frankly it is rare to use a detector as the glass will usually arrive on site with Pilkington K Glass "stickers" on the sealed units. These stickers" also tell the installer which side of the glass unit should face inwards. Some installers will give you the "stickers" as proof. (This I recommend) I suggest they are kept safe and given to any new owners of your property as proof also. Sometimes you can visually detect the K coating but this is more difficult. I quote below what Pilkington themselves have to say...." Pilkington K Glass has high light transmission and appears virtually the same as clear float glass. However, in rare instances of strong oblique lighting, the coating may be seen as a transparent film. This is simply a transient visual effect which can be considered positive evidence of the coated surface being present. Further evidence of the coating's presence is through the very minor effect it has on white light transmission. This effect is so small as to be generally unnoticeable However, when a light coloured object or material is in close proximity to the glazing, dependent on local circumstances and conditions, a slight darkening can be noted." 

Question submitted by Mark

I am looking to use Pilkington K glass. I have however been warned that it will reduce the clarity of the glass and hence give a cloudy view out when the sun is at certain angles. Please can you give me some more detail on this.

This Question answered by Tina Dunlop @ Almost Impartial Guide - It is true that Pilkington K Glass is very slightly "tinted" Pilkington mention this in their literature and claim (quite rightly in my opinion) that the effect is negligible. In fact I would say very few people would notice it and those who do might be grateful to have such an effect in a conservatory. It sounds to me as though someone is trying very hard to persuade you not to have K Glass. Personally I would way up the many benefits of Pilkington K Glass (extra insulation / more likely to be able to use room all year round) versus what I can only perceive of as a very minor possible disadvantage. I have K Glass installed in my own conservatory at home and have never experienced any cloudy effect.



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