Window Film Performance: Separating Fact from Fiction
As a long-time partner with Solar Gard UK, I've seen firsthand the incredible benefits of quality window film. But I've also witnessed the frustration and disappointment that arises from inflated or misleading performance figures in the industry. It's time to address this head-on.
The Problem: Misleading Numbers and Opaque Data
It's infuriating when companies tout unrealistic heat reduction percentages, often by blurring the lines between Total Solar Energy Rejection (TSER) and actual Heat Gain Reduction. TSER is a broad measurement of energy rejected across the light spectrum, but it doesn't always translate to real-world heat reduction.
What's worse, many companies base their performance figures on outdated 3mm single glazing. Let's be honest, how many of those windows are still around in the UK in 2026? Applying those numbers to modern Low E argon double-glazed windows is simply misleading.
Why This Matters
When customers expect a significant reduction in heat on a scorching day and don't experience it, they immediately think the product is worthless. This hurts the entire industry and undermines the potential benefits of window film.
The Solar Gard Difference: Transparency and Accuracy
What I've always appreciated about Solar Gard is their commitment to transparency. They provide performance figures for single, double, and even triple glazing. They also clearly state the Solar Heat Gain Reduction percentage. And if you're still skeptical, their data is independently verified by the National Fenestration Rating Council (NFRC).
For context, our highest performing film on double glazing, the externally fitted DX05 OSW, offers an 87%* Heat Gain Reduction (*when fitted to triple glazing). It's dark, reflective, and delivers exceptional performance.
Spotting the Red Flags
When a potential customer tells me a competitor is promising over 60% heat reduction with a medium-tinted internal film on their brand new Low E argon double-glazed windows, I know they're likely being misled.
Here's what to watch out for:
- Unknown Brands: Be wary of rebranded or custom-made spec sheets. You have no idea what you're actually getting.
- Shared Columns: If a spec sheet combines "Total Solar Energy Rejected" and "Heat Reduction" into a single figure, run the other way. These are two different measurements.
- Missing Context: Always ask what type of glass the performance figures are based on.
My Approach: Education and Honest Comparisons
When I suspect a customer is being misled, I find the nearest equivalent film in our Solar Gard range and send them the spec sheet. I highlight the performance data for single, double, and triple glazing.
For example, I might show that our comparable film reduces heat gain by 44% on clear double glazing (not 65% as the other company stated). And I emphasize that this figure is for clear double glazing, not modern Low E argon double-glazed glass, which can further reduce performance by 10-20%.
I also point out the G-value (solar heat gain coefficient) on our spec sheet. The lower the G-value, the more heat reduction the film can achieve. If our film has a lower G-value than the competitor's, but they're claiming higher performance, something doesn't add up.
An Industry-Wide Problem
This isn't just about one company or one product. It's an industry-wide issue. If reps and literature are incorrect, how can new window film companies be expected to provide accurate information?
The Solution: Demand Transparency
As consumers, we need to demand transparency. Ask questions, compare spec sheets, and look for independent verification. Don't be afraid to challenge claims that seem too good to be true.
By educating ourselves and holding the industry accountable, we can ensure that customers get the performance they expect and deserve
