Will Window Film Cause My Glass To Break?

Will Window Film Cause My Glass To Break?

Window Film and Thermal Stress 

So many San Francisco Bay Area customers ask: Does window film cause glass to break? We explain below.

“Will window film cause my glass to break?” This is one of the most frequently asked question we receive from our potential customers. As our recent post about window film myths mentioned, this is a common concern. Many in the San Francisco Bay Area have been led to believe that window film causes thermal stress glass breakage. Why does this misconception exist? It is based on the fact that window film can increase the thermal stress on the glass due to sunlight.  However,  the misconception does not take into account a few factors. Factors like the relative strength of glass and the heat tolerances of different types of glass need to be considered.  Also, there are techniques that window film manufacturers and installers take to avoid the risk of thermal stress breakage. 

While it is true that glass can break under certain circumstances, the occurrence of thermal stress breakage in residential and commercial windows is quite rare. To mitigate any potential risks, window films are designed with film-to-glass thermal stress compatibility guidelines that take into account the different types of glass. By adhering to these guidelines, the chances of thermal breakage caused by window film are extremely low. In order to provide a better understanding of how thermal glass breakage works and how we address the thermal strengths of windows, continue reading.

What is Thermal Stress

Thermal stress is caused when glass is exposed to excessive temperature variation. The greater the temperature difference, the greater the thermal stress. Temperature differences in window glass are generally caused by the way sunshine affects a window. Different parts of the window receive different amounts of sunlight and heat. For instance, the center of a window gets direct sunlight and the edges get less. The sun’s energy warms the center of the window, causing it to expands. This puts pressure on the cooler edges to also expand. If this pressure exceeds the breaking strength of the glass, it can fracture. 

Different Glass, Different Strengths

Different types of glass have different strengths. For instance, tempered glass is so strong that it will only suffer thermal breakage due to fire.  Because of this, it is often used in many architectural applications. This includes storefront windows and doors. Heat-strengthened (also known as “thermally toughened”) glass is also exceptionally resistant to thermal stress. It amazingly has a temperature difference threshold of almost 500 degrees Fahrenheit! Temperature difference thresholds for other glass types include:

  • Annealed and float glass—about 105 °F 
  • Roughcast glass—about 86 °F
  • Wired, polished or cast glass—about 77 °F

In general, thermal breakage is not a concern with tempered and heat-strengthened window glass. However, it does need to be considered in relation to other window glass types.

Window Film and Thermal Stress 

Window film experts like ClimatePro are very familiar with thermal stress. We conduct a detailed film-to-glass compatibility evaluation. This happens before beginning any window film installation. This evaluation considers many factors, including glass type, color, pane size, and thickness. We also consider external shading, window coverings, frame type, altitude, and solar energy intensity. The film-to-glass compatibility evaluation also needs to review other important window film properties.

Additionally, the evaluation must consider the window film’s solar-optical properties. These properties can vary depending on the specific film and the unique characteristics of the glass it will be applied to. This assessment is crucial in determining the risk of thermal stress breakage and ensuring the compatibility of the film with the glass.

Window film manufacturers include film-to-glass thermal stress compatibility guidelines with their products. Installers can quickly assess the compatibility of a specific film for your window. Professionally assessed Window film applications reduce the risk of thermal stress breakage. Remember, glass can naturally break. Hence, we can never provide a guarantee against thermal breakage. However, thermal breakage is typically covered under the warranties we offer with our window film work.

ClimatePro: Your Window Film Specialist

Looking for privacy, security, UV protection, glare reduction, decorative, or heating and cooling window? Interested in adding the benefits of window film to your home or business but still concerned about thermal breakage? Contact us today for a free consultation. We have offices in North Bay, San Francisco, and San Jose. We can be reached at (707) 569-9098.