Haze is an optical phenomenon which makes the glass look like it is covered in a very fine, uniform layer of dust when viewed from an oblique angle or viewed under strong light incident on the glass at an oblique angle. Our original Pilkington K Glass™ can, under certain lighting conditions, display this phenomenon to a limited extent. 

The reason for this is that the Pilkington K Glass™ coating is not as smooth as the glass surface. While this is not obvious to the eye when examining the glass, some people who regularly handle Pilkington K Glass™ can tell which side the coating is on by the feel of it. 

The optical effect of the slightly rougher surface is to scatter a small proportion of the light incident on it (in exactly the same way as a thin layer of dust would, which is why it looks similar). With Pilkington K Glass™ the amount of scattered light is generally less than half of one percent of the light coming through the window, so under most viewing conditions it is not obvious. However, when incident sunlight is at an oblique angle and the view through the glass is of a shaded area, then the scattered light can become more visible, giving rise to the appearance of haze. 

Nowadays low-emissivity glass is coated using alternative technologies so that our latest low-emissivity glass products such as Pilkington K Glass™ S and Pilkington Optitherm™ S1 Plus are less susceptible to this phenomenon.