A cooler home on hot summer days starts with the right window glass
You may have experienced rooms in your home becoming uncomfortably warm when the sun shines directly through the windows. To reduce the heat, you might close the blinds or curtains — making the room darker and limiting the view outside — while still relying on fans or air conditioning to feel comfortable. What you may not realize is that the type of glass used in your windows can influence how much solar heat enters your home.
Why the glass in your windows matters
When people think about windows, they often focus on the frame, color or opening style. Because glass represents around 80% of a window surface, it plays an important role in how heat and daylight enter your home, and how the window performs.
Different types of glass are designed to respond to different needs. Some help retain warmth inside during colder periods, while others help limit the amount of solar heat entering the room during sunny weather. Some types of glass can even combine several of these functions — and more, such as safety and security, and noise reduction — in the same window. Choosing the right glass can therefore contribute to the overall comfort of your home.
Up to 11°C cooler indoors
An independent study comparing two identical rooms
To better understand how glass can influence indoor temperature, an independent study was conducted by Group14 Engineering*. Measurements were taken on a typical hot summer day (July 21st, 2025).
The study compared two identical rooms under the same building and climate conditions, without any cooling equipment operating in the rooms. Each room had a floor surface of 20 m² and a total window surface of 8 m². Both rooms had the same orientation: south west orientation in most locations and south orientation in Vienna.
The only difference between the two rooms was the glazing used in the window:
- one room used standard thermal insulation glazing
- the other used Guardian Sun™ solar control glass
By comparing these two situations under the same conditions, the study evaluated how different glazing types can influence indoor temperature.
What the study shows
The results indicate that glazing using Guardian Sun solar control glass can help significantly reduce indoor temperatures on hot summer days compared with standard thermal insulation glazing.
Depending on the location and climate conditions, the simulations showed potential indoor temperature reductions such as:
- Athens: up to 10°C lower
- Rome: up to 11°C lower
- London: up to 11°C lower
- Lyon: up to 10°C lower
- Vienna: up to 6°C lower
- Wroclaw: up to 4°C lower
Why solar control glass can make a difference
Solar control glass is a type of window glass designed to reduce part of the sun’s heat before it enters the room, while still allowing natural daylight to pass through the window.
By limiting some of the solar heat entering the building, this type of glass can help keep rooms more comfortable during warm weather and helps reduce or even avoid the need for cooling in some cases.
Compared with standard glazing, solar control glass may also help reduce the need to close blinds during the day, allowing daylight and views to be maintained.
Glass can support comfort in different ways
Managing solar heat is only one of the ways window glass can contribute to comfort inside your home. The glass used in your windows can influence several aspects of comfort and performance in your home. Depending on the combination of glass used, windows can help:
- Stay cool during the summer
- Keep warmth inside during colder months
- Improve safety and security
- Reduce energy consumption
Helping you choose the right glass for your windows
Choosing window glass can sometimes feel complex. Different types of glass offer different benefits depending on your home, climate conditions, and comfort needs.
To help simplify this decision, Guardian Glass has developed practical guidance and simple tools to help you make a decision.
* “Energy Modeling of Internal Room Temperatures For Guardian Glass, Phase 1, November 11, 2025”, and “Energy Modeling of Internal Room Temperatures For Guardian Glass, Phase 2, December 16, 2025”.