Overview of types of glass used in double-glazed windows

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Plastic windows appear with incredible speed in the “eyes” of buildings, be it a government institution or a private house. People prefer PVC windows, as they are confident in their heat-shielding properties, not to mention other advantages. Manufacturers of plastic windows strive to enhance the useful properties, so they use special glass for double-glazed windows. These are K-glass and i-glass. What are the advantages of K-glass and i-glass?

Overview of types of glass used in double-glazed windows

What is float glass

To begin with, let’s deal with the usual glass of double-glazed windows: float glass. This is a common type of glass made by cooling on a thin sheet of tin. The production of float glass takes place in 5 stages: preparation of the raw material, melting of the raw material, formation of the glass surface, annealing of the glass plate, cooling the glass.

Low-E float glass

Due to the fact that the molten glass is cooled in a bath with a layer of liquid tin, its optical properties increase, a standard thickness is formed, and there are no optical defects. The glass is very transparent and smooth, but the energy-saving properties are quite low.

Issue issue

The fact is that thermal protection is based on three indicators: convection, thermal conductivity and heat radiation. Double glazing (double-glazed windows) is used to enhance thermal insulation during convection and thermal conductivity. But energy saving is determined by low heat radiation.
Each glass has a certain emissivity (E) – the ability of glass to emit long heat waves and transmit short waves into the room. The lower the emitter, the higher the energy savings. For example, for ordinary glass, the emissivity value is 0.835, and for selective glass (as i-glass and K-glass are called) – 0.04 and 0.2. The difference is significant! Therefore, it is very important to make the right choice of glass for insulating glass units..

Features of K-glass

K-glass is an upgraded Low-E float glass, which means “hard coating”. Hard deposition of metal oxides on the glass surface increases its energy-saving properties, reducing the emissivity. In float glass production, when it is hot, a thin metal oxide film is applied by pyrolysis. Due to the fact that the atoms of the glass and the metal oxide interact, a resistant coating is formed that is not afraid of mechanical damage. To enhance heat-shielding characteristics, K-glass can be tempered and laminated.


The use of K-glass assumes a single-glazed unit, as it has low-emission characteristics. All the heat from the heaters is returned back to the room, which reduces heating costs. K-glass passes the energy of short-wave solar rays inside the room and does not allow it to leave in the form of long radiant waves.

The untreated side of the K-glass faces the room, and the side with the oxide coating faces the interior of the glass unit. Thus, improved glass at low degrees outside (- 25) and normal room temperature (+25) has a temperature of +11 on the inner surface (compare, for ordinary glass +5).

As for the appearance, here K-glass is not inferior in transparency to float glass and i-glass. It is the same smooth, even and light-conducting.

I-glass advantages

i-glass represents a new generation in the glass industry. It is similar to K-glass, but has a higher performance. A double layer of low-emission metal oxide spraying is applied to the surface of the float glass. This technological process takes place in a vacuum equipment with a magnetron sputtering unit. The metallized film is, as it were, magnetized to the glass layer. This method of spraying is considered “soft” and is called Double Low-E.


Since the coating of i-glass is considered “soft”, its abrasion resistance is poor in contrast to float glass and K-glass. i-glass must be handled with great care. The energy saving characteristics of super glass are at a very high level. If the emission coefficient of K-glass is 0.2, then for i-glass it is only 0.04. And this means that i-glass retains up to 90% of the heat in the room, reflecting long-wave radiation. As for the temperature on the glass surface at -25 on the street and +20 in the house, then its indicator is + 14.

i-glass has high light transmittance and transparency. If we take as a basis the fact that 0 is equal to black, and 100 is neutral, this indicator for i-glass is 98 (for K-glass it is 99). To prevent damage to the energy-saving coating, the surface of the i-glass is directed towards the inside of the glass unit.

i-glass is the latest advancement in the glass industry. It is successfully used in the production of insulating glass units for plastic windows in America and Europe. Unfortunately, Russian industrialists still cannot produce i-glass and buy it abroad. By itself, i-glass is an expensive pleasure, and bringing it from abroad increases the price several times. But over time, the cost of i-glass pays off with lower costs for heating the room.

The advantages of K-glass and i-glass are obvious. You just need to weigh everything, calculate when choosing glasses for double-glazed windows and do not forget that the avaricious pays twice. Take care of your health and wallet!

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