Glass Glossary

Emissivity


Last Updated: November 23, 2023

Emissivity is a measure of the ability of a material’s surface to emit thermal radiation (infrared radiation) relative to a perfect emitter, known as a black body. It is a critical concept in the context of the window and glass industry, especially when evaluating the energy efficiency of windows. Emissivity is represented by a value between 0 and 1, with a value closer to 1 indicating a higher ability to emit thermal radiation, and a value closer to 0 indicating a lower ability. Emissivity values are essential in determining the performance characteristics of a window, including its ability to retain heat in the winter and prevent excessive heat gain in the summer.

Low-emissivity coatings like Cardinal’s LoĒ™ are thin metallic coatings applied to the surface of the glass, reducing the emissivity of the window. LoĒ coatings help reduce the amount of heat transferred through the window by reflecting thermal radiation away from the surface, improving the energy efficiency of windows. These coatings can be applied to one or more surfaces of the glass in an insulating glass unit (IGU), and their performance varies depending on factors such as the number of layers in the coating, the specific composition of the coating and the position of the coating within the IGU.