Understanding Thermal Stress in Glass and How Window Film Can Help
Glass is a remarkable building material, but it’s not immune to the effects of temperature. One factor that can compromise glass integrity is thermal stress, which occurs when different parts of a window experience uneven temperatures. At The Tint Shop, we consider thermal stress a key factor when recommending or installing window films for homes and commercial buildings.
What Is Thermal Stress?
Thermal stress refers to the pressure exerted on glass due to temperature differences across its surface. For example, a window exposed to direct sunlight in the centre may become significantly warmer than its edges, which are shaded by the frame. As the sun-heated glass expands, it pushes against the cooler edges, creating stress. If this stress exceeds the glass’s breaking strength, it can lead to thermal breakage.
Even in everyday environments, this phenomenon can occur with large panes of glass or highly reflective surfaces, particularly when the glass is exposed to intense solar energy.
How Different Glass Types Handle Thermal Stress
Not all glass reacts to thermal stress in the same way. Understanding the relative strength of different types is essential:
- Tempered glass – extremely strong; typically only suffers thermal breakage in extreme conditions such as fire.
- Heat-strengthened glass (thermally toughened) – highly resistant; can tolerate temperature differences of up to nearly 500 °F.
- Annealed or float glass – threshold of approximately 105 °F.
- Rough cast glass – threshold of around 86 °F.
- Wired, polished, or cast glass – threshold near 77 °F.
Generally, thermal breakage is rare with tempered or heat-strengthened glass but may be a concern for other types, particularly in high-sunlight or large-pane applications.
Why Window Film Specialists Consider Thermal Stress
Professional window film installers, such as those at The Tint Shop, conduct a film-to-glass compatibility evaluation before applying any window film. This assessment ensures that the chosen film will not inadvertently increase thermal stress. Factors examined include:
- Glass type, thickness, colour, and pane size
- Frame type and any shading or coverings
- Altitude and intensity of solar exposure
- Window film properties, including solar energy transmission, reflection, and absorption
Absorption is particularly important: films that absorb more solar energy can increase surface temperature and, if not carefully matched to the glass type, may raise the risk of thermal stress.
Fortunately, leading window film manufacturers provide thermal stress compatibility guidelines, which allow installers to select the most suitable film for each window. When professionally assessed and installed, the risk of thermal breakage is exceptionally low.
Protecting Your Windows
While glass inherently has limits, a proper film-to-glass evaluation, combined with high-quality window films, ensures that your windows remain safe, functional, and long-lasting. Additionally, many window film warranties include coverage related to thermal stress, offering extra peace of mind.
At The Tint Shop, we prioritise safety and performance in every installation, helping you enhance comfort, reduce glare, and improve energy efficiency without compromising the integrity of your windows.