Why Glass Type Matters When Applying Window Film (And How to Avoid Cracks)
When people reach out to us about window film, most of the time they’re focused on the outcome — heat rejection, privacy, glare reduction, UV protection. But what often gets overlooked is the starting point: the glass itself.
At Film Bros, we always begin our process with a consultation — not just to take measurements, but to actually identify what kind of glass you have. Why? Because not all glass behaves the same when you apply film to it. And ignoring that can cost you more than just performance — it can literally shatter your window.
Let’s break down the types of glass we encounter most, and what that means for your window film options.
1. Annealed Glass
Your basic, everyday residential window.
This is the most common type of glass we see in homes, especially older ones. It's not tempered or treated — which means it’s more fragile. If the wrong film is applied to it, especially one with high solar absorption, it can lead to thermal stress and eventually cracking.
What to know:
We use film-to-glass compatibility charts to make sure only low-absorption films are applied here.
Reflective or dark films? Usually a no-go unless you're using exterior-grade options.
2. Tempered (or Toughened) Glass
Heat-treated for strength and safety.
Tempered glass is about four to five times stronger than annealed. If it breaks, it shatters into small, less dangerous pieces — which makes it ideal for doors, bathrooms, and commercial settings.
Why it matters:
Tempered glass can typically handle more aggressive films, including darker tints and reflective options.
That said, it still has to be evaluated on a case-by-case basis — especially if it's partially tempered or has unique coatings.
3. Double Pane / Insulated Glass Units (IGUs)
Two panes of glass with a sealed airspace in between.
These are super common in modern condos and newer homes. The thing is, adding film to these windows without doing your homework can mess with the pressure inside the unit — leading to seal failure, condensation, or even breakage.
What we look for:
We check the spacer bars (the little metal strip between the panes) and look for low-e coatings.
If it’s a low-e coating on surface #2, for example, it changes what film we can apply.
4. Laminated Glass
Two sheets of glass with a plastic interlayer.
This type of glass is commonly used in skylights, hurricane zones, and high-security applications. It’s designed to stay in one piece if broken — like a car windshield.
Why this matters:
Laminated glass can trap heat differently, especially with film applied.
We usually lean toward exterior films to keep the heat absorption on the outside.
Safety films or security tints can also be used to reinforce an already-strong structure.
5. Low-E Glass (Low Emissivity)
Coated to improve energy efficiency.
Low-E coatings reflect infrared energy (heat), helping keep heat inside during winter and outside during summer. But when you apply film, you have to be very careful — because these coatings are sensitive, and applying film over them incorrectly can totally kill their performance.
What we do:
Use a laser meter to detect which surface the low-e coating is on.
Then we determine which films will complement — not conflict — with the existing setup.
6. Wired Glass
Glass with metal wire mesh inside — often seen in old commercial buildings.
This stuff is surprisingly fragile. The wire doesn’t make it stronger — it’s there for fire protection. And because it has different thermal properties, it’s super prone to cracking with the wrong film.
Rule of thumb:
We proceed with extreme caution or recommend alternatives.
The New Build Problem: Shifting Foundations & False Blame
Something we’re seeing more and more is homeowners in newly built homes being told by their builder or contractor that the film cracked their glass.
Let’s clear this up.
The reality is, with how fast new homes are being thrown up these days, foundational settling is a real thing — and it happens sooner than most people expect. That shift can impact your windows, doors, flooring, and even drywall seams. If your house is less than 5 years old, and you’re noticing cracks or stress around your windows, it’s not automatically the film’s fault.
In fact, at Film Bros, we’ve never had a single case of window cracking caused by our film — and that’s because we take the time to inspect your glass thoroughly before we apply anything. We use laser meters, film-to-glass compatibility charts, and visual checks for stress points. If someone else installed your film and did go through that same process — if they metered the glass, chose film within spec, and followed best practices — then odds are the film wasn’t the issue. It was probably a structural problem that was already developing.
We’ve been brought in to assess jobs where the film was blamed — and more often than not, we find that the house was shifting, the glass was under frame pressure, or the window had a flaw that predated any film install.
This is exactly why we’re so cautious, especially with new builds. It's not just about performance — it’s about protecting your investment.
Why It All Comes Back to the Consultation
We don’t just show up with a roll of film and start cutting. Every window tells a different story — and our job is to read it properly before we apply anything. That’s why we always start with a free consultation where we:
Identify your glass type
Check for coatings and thermal properties
Look for signs of structural stress
Match film that’s not just compatible — but optimized
Bottom Line: The Wrong Film on the Wrong Glass = Problems
From cracked windows to failed seals to heat buildup, the consequences of skipping this step are real. But when it’s done right? You get the best of both worlds: performance and peace of mind.
Based in the GTA? Let’s Talk.
If you're in Toronto or the surrounding areas, and you're looking for heat rejection, privacy, or security film — we’ve got you. Just hit the link below to book a free consult and we’ll make sure your windows are ready for film.
