Households are being warned that an everyday home heating method—applying window film to retain warmth—can shatter glass if the wrong type is chosen. Thermal stress, caused when different sections of a glass pane heat up or cool down at varying rates, can lead to cracking when temperatures diverge significantly.
Why window film can damage glass
Tomass Kundzins, window film expert at Glacier Tinting, explained: "Some films absorb more solar energy than others, which can change how the glass heats up when sunlight hits it. If the film isn't suitable for that particular window, it can increase the risk of the glass cracking."
He added: "That doesn't mean fitting window film is dangerous, it just means the right film needs to be matched to the right glass."
Solar-controlled film enhances heat absorption, and if the temperature variation becomes sufficiently high, it can result in cracking.
How to choose the right film
The first step is to establish whether your windows are single, double or triple glazed, and determine if they feature any existing coatings. Read the manufacturer's compatibility guidance on any window film you purchase, as certain products are only appropriate for specific glazing types.
Kundzins said: "Two windows can look almost identical, but that doesn't mean they have the same glass specification. One might have a coating or be made from a different type of glass, and that can affect which films are suitable."
He advised: "Make sure you find out what you've actually got before ordering anything. If you're not sure, ask the window manufacturer or a professional film installer to check."
Cheap film can be a costly mistake
The appealing option is to purchase inexpensive film that provides warmth without straining finances, but without proper research you risk causing thermal stress to your glass.
Kundzins warned: "Be wary of buying film purely because it's cheap or has good reviews. A film might work perfectly well on one person's windows and be completely unsuitable for somebody else's."
He also noted: "You should also check whether applying the film could affect any existing glazing warranty, particularly if your windows are relatively new."
