To make Low-E glass, certain properties such as the iron content may be controlled. Also, some types of glass have natural Low-e properties, such as borosilicate
). Specially designed coatings, often based on metallic oxides, are applied to one or more surfaces of insulated glass
. These coatings reflect radiant infrared
energy, thus tending to keep radiant heat on the same side of the glass from which it originated. This often results in more efficient windows because: radiant heat originating from indoors is reflected back inside, thus keeping heat inside in the winter, and infrared radiation from the sun is reflected away, keeping it cooler inside in the summer.
In typical insulated glazing
, the low-e coating is found on one of the interior faces of the glass. A simple low-e coating helps to reduce heat loss but allows the room to be warmed by any sunshine. If solar control is required then the outside pane of glass would have either a film or a body tint to reflect solar radiation. The principle of operation is similar to the way selective wavelength transmission of glass or other glazing helps warm a greenhouse, popularly known as the greenhouse effect
, in which short wavelength radiation is transmitted through the pane, but longer wavelength radiation absorbed rather than transmitted. However, low-e glass reflects the radiation rather than absorbing it, improving performance compared to the glass in a simple greenhouse.