Why should we remove the low-E glass coating in IGU production?

More and more people are familiar with insulating glass, and also know better about Low-E glass. The glass processing companies are always talking about Low-E glass tempering furnace, or Low-E glass insulating glass washing machine.

However, do you know why should we remove the low-E glass coating in IGU?  Or which side should be inside IGU?

In order to understand the reason, we need to know first: what is Low-E glass? How many kinds of Low-E glass?


Low-emissivity glass (or low-e glass as it is commonly referred to) is a type of energy-efficient glass designed to prevent heat escaping through your windows to the cold outdoors in cold area, or prevent the heating outdoors to coming through your windows to indoors.

(Low emissivity (low e or low thermal emissivity) refers to a surface condition that emits low levels of radiant thermal (heat) energy.)

How Low-emissivity Glass works

Heat always flows towards the cold. Therefore, window glass without a low-e coating will absorb the heat from your home and radiate it onto the colder outside surface, where it is lost. Low-e glass has a special coating which is a poor radiator of heat and does not allow heat to be transferred to the outside. Instead, the low-e coating actually reflects the heat back into your room.

In the winter the low-e coating acts to keep heat in by reflecting back the heat carrying far infrared light.

If you are in summer weather near equator, you are saving the AC electricity consumption with Low-E glass which prevent the heating outdoors coming through windows.

Which Low-E side should be face inside IGU?

There are online or offline Low-E glass, in order to protect the low-E coating glass film, most of the Low-E coating side should be the inner side of IGU.

In a double insulating glass, should the inner glass or outer glass be the low-E coating glass?

In a standard double panel IG there are four potential surfaces to which coatings can be applied: the first (#1) surface faces outdoors, the second (#2) and third (#3) surfaces face each other inside the insulating glass unit and are separated by a peripheral spacer which creates an insulating air space, while the fourth (#4) surface faces directly indoors. Passive low-e coatings function best when on the third or fourth surface (furthest away from the sun), while solar control low-e coatings function best when on the lite closest to the sun, typically the second surface.

However, the lowe-E coating is used almost exclusively on the inner surface of a dual pane sealed unit. It functions to reduce solar heat gain in the summer and retain heat in the winter. Low-e coating works by blocking both the shorter UV light and the longer infrared light. Soft coat low-e two coatings blocks about 70% of the infrared and 80% of the UV light from entering through the glass.

What is the coating surface made of?

Low-E Glass has a thin layer of oxidized metal or metals on one side The thermal emissivity of various surfaces is listed in the following table.

Materials surfaceThermal emissivity
Silver, polished0.02
Aluminum foil0.03
Marble, smooth0.56
Paper, roofing or white0.88 to 0.86
Plaster, rough0.89
Marble, polished or white0.89 to 0.92
Concrete, rough0.91
Glass, smooth (uncoated)0.91

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