faceboo Choosing the Right Glass For Facade & Glass Windows

Science of choosing the right glass

May 16, 2022
Last updated on August 12, 2023

K-Value, U-Value, R-Value, C-Value

When it comes to buying glass for facades or windows, it boils down to two crucial choices one must make – its thermal insulation type and thickness. Before we look at the thermal insulation one should consider, it is important to understand the thermal properties of glass. Using incorrect glass and improper installation leads to poor performance, i.e. reducing the glass’s capacity to insulate the house, when exposed to gradual or sudden temperature changes. Thermal properties determine the performance of glass in different conditions. Using this information, you can select the right glass composition for your home and environment.

low e glass

© JKMDC Architects and Planners. Project - Breathing House, Kottarakkara

One of the primary features of glass used as a thermal insulation material is its ability to reduce the heat exchange between two surfaces or the surface and environment. Glass, or any other material, used for insulation should have low thermal conductivity. You may be wondering why there are so many values - K-Value, U-Value, R-Value, and C-Value - you should consider if it is this simple. In this article, we will define the concepts using simple terms to help you make the right decision when it comes to purchasing glass.

There are many terminologies with respect to insulation and it can be overwhelming to understand them all. While one is not always expected to know all the technicalities with respect to glass and its properties, it certainly helps to know some of the basics.


Also known as insulation k-value, this factor describes the thermal conductivity of glass. It determines the ability of glass to retain heat, independent of the thickness. A lower k-factor is better since it indicates that the glass does not let heat escape through it. If you live in colder environments, a glass with a lower k-factor will ensure the heat remains trapped in your home keeping you comfortable and warm.

thermal insulation glass

© NMA Architects. Project - House for Vishal and Rekha Bharadwaj, Mussoorie by NMA Architects


The C-Factor, also known as insulation C-value, determines the thermal conductance of glass. This factor is dependent on the thickness of the glass and considers the number of units of heat passing through the material. The C-value, unlike the K-value, is inversely proportional to the thickness of glass, and therefore, you must choose glass with a lower C-value for better insulation.


Also known as insulation U-value, this factor measures thermal transmittance. Thermal transmittance is dependent on the temperature differences between the indoors and environment and determines the amount of heat transmitted through the glass. The lower the value, the better the glass. Low Emissivity (Low-E) glass has a lower U-factor. While it allows sunlight to pass through easily, it will prevent infrared and ultraviolet rays from entering your home.


The R-Factor uses the information from all other factors, making it easier to judge the overall capacity of glass to insulate your establishment. It stands for thermal resistance, and the higher the factor, the better the insulation. This factor measures how effectively the material blocks heat instead of radiating it.

It can be difficult to put these terms into layman words, but you must know the following when it comes to these factors:

  • A lower R-factor and C-factor indicate that the glass can be used for insulation. These glasses are best used in colder climates, so you can use them in cities like Shimla and Manali
  • A lower K-factor indicates that the glass has a higher insulating value for a specific thickness
  • A lower U-factor indicates that the glass can insulate effectively. This indicates you can control the heat inside the building by using glass with a low U-factor, and therefore, can be used in cities like Chennai and Jaipur

It is important to note these factors are specific to glass and other materials used for insulation. Understanding of these factors goes a long way towards making efficient and informed choices.

About Author

Soumya Rajagopalan is a freelance writer and has written eBooks on different topics, including lifestyle, health and nutrition, and more. She also works as an information risk consultant.




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