Which window film blocks the most heat?

If maximum heat rejection is your goal, the top performers are reflective (metallised) solar films and high-end spectrally-selective ceramic films, with the best rejecting up to 79% of total solar energy. But the film that blocks the most heat isn't automatically the film you should choose — the right answer balances rejection against how clear you want the glass to stay.

Here's how to compare films properly and pick the best one for your room.

The number that matters: TSER

Ignore the marketing and look for one figure: Total Solar Energy Rejected (TSER). It captures the whole picture — how much of the sun's total energy (across visible, infrared and UV) the film stops. A film with 70% TSER blocks more heat than one with 55%. It's the single most useful number for comparing films.

You'll also see VLT (Visible Light Transmission) — how much daylight comes through. High TSER with reasonably high VLT is the sweet spot: lots of heat gone, room still bright.

Reflective (metallised) films

These reject the most heat and give the glass a mirrored look from outside during the day. That mirror effect is often a bonus — it also delivers strong daytime privacy, which makes reflective films a great two-in-one for overlooked, sun-facing rooms, shopfronts and offices. The trade-off is the visible reflective appearance, which not everyone wants.

Spectrally-selective ceramic films

Premium ceramic films are the clever option: they're engineered to reject the infrared (heat) and UV while letting most visible light through, so they achieve very high heat rejection while staying much clearer than reflective films. If you want maximum heat control but need the glass to look essentially unchanged — a period home, a feature window, a bright living space — this is usually the pick. They cost a little more, but the near-invisible finish is worth it to many people.

Why 'most heat blocked' isn't always right

The strongest film isn't automatically the best choice. A heavily reflective, high-rejection film on a north-facing window that barely gets sun is overkill and just darkens the room. Orientation matters: south and west glazing justifies the strongest films; east less so; north rarely needs much.

The look matters too — a mirrored film transforms a façade's appearance, which is great for some buildings and wrong for others. The best film is the highest rejection that still suits that window's orientation and the appearance you want.

How we choose it for you

On the survey we look at each window's orientation, size, glazing and the problem you're solving, then recommend the film with the right TSER and look — not just the biggest number. Often a home ends up with a stronger film on the south/west elevations and a lighter one elsewhere. Try our Heat Reduction Calculator for an indicative sense of what different grades achieve on your glass.

The bottom line

For the most heat blocked, reflective and premium ceramic films lead, both up to around 79% TSER — reflective for maximum rejection and privacy, ceramic for near-invisible performance. The right one for you depends on orientation and looks, which is what the survey sorts out. Book one free and we'll match it.