What “Heat Rejection” Numbers on Window Tint Actually Mean

Three numbers, three measurements, three different realities

Any professional film carries a Product Data Sheet (PDS) — the lab-measured spec table the manufacturer publishes. For every shade of every film it reports a handful of columns: VLT (how much visible light passes), UV rejection (always above 99% on quality films), and the three heat-rejection metrics people confuse constantly.

The solar spectrum, and why the number depends on which part you measure

Sunlight reaching a windshield breaks into roughly 3% ultraviolet, 44% visible light, 53% infrared. Every rejection figure is a percentage of a different slice:

• TSER is the share of the whole 100%. A 60% TSER means the film turns away 60% of all incoming solar energy.
• IRER is the share of the 53% infrared slice. A 65% IRER means the film turns away 65% of the infrared — which is roughly 34% of the total.
• SIRR is the share of a narrower band inside that 53%. A 93% SIRR over 900–1000 nm means the film rejects almost everything in that specific slice — but infrared energy is distributed across 780–2500 nm, so a narrowband measurement is not a whole-infrared number.

The honest comparison is apples-to-apples: TSER against TSER, IRER against IRER, SIRR against SIRR. The dishonest comparison is the one shoppers routinely make — the ceramic film's SIRR against the untinted glass's TSER, which inflates the apparent improvement by a factor of two or more.

The same film at the same shade, three different numbers

The Avery Dennison Encore Automotive Window Films PDS publishes all three figures for every shade of every tier. Here are the three ceramic tiers at a representative mid-range VLT (around 35%), on the same film, same shade, same test — just three different measurements:

Source: Avery Dennison Encore Automotive Window Films, Product Data Sheet Rev. 01 (2025-09-03). Avery Dennison calculates these on NFRC methodology, LBNL Window 5.2, on 1/4" (6mm) clear glass, subject to variation within industry standards — they describe the film, not a promise about a particular vehicle. Your glass, its thickness and its own factory tint all affect the finished result.

Encore Supreme at 36% VLT shows TSER 54 and SIRR 84. Both are honest figures the manufacturer publishes side by side. Quoted alone, the SIRR “rejects 84% of infrared” feels like a different product than the TSER “rejects 54% of total solar energy” — but they describe the same film at the same shade, with no asterisk hiding anything.

This is why the industry's recurring overstatement is not technically a lie — it is a quoting-the-flattering-column habit. A shop that advertises “up to 93% heat rejection” and installs Encore Supreme IR is not inventing numbers. They are printing the SIRR column and labelling it “heat”, which is a thirty-point overstatement against the TSER you will actually feel.

Why the narrow-band SIRR number is always higher

Infrared radiation is not one wavelength. It spans roughly 780 nm to 2500 nm in the solar context, and different films handle different parts of that range with different efficiency. Nano-ceramic particles are engineered to work well across the near-infrared band where the solar energy density is highest — somewhere around 900–1200 nm. Further out into the mid-infrared, where ambient thermal radiation lives, films perform less consistently.

SIRR — Selective Infrared Rejection — is measured over the narrow band where the film performs best. On a ceramic film that is 900–1000 nm; on a metalized film it is a different slice. The number is accurate, but it describes the film's best 10% of its infrared range, not the full 1720 nm the spectrum actually covers.

IRER is the honest infrared figure for comparison because it is integrated across the whole band — 780 to 2500 nm. For Encore Supreme at 36% VLT it is 59, not 84. That is still a serious improvement over the ~15% an untinted window achieves. It just is not 84.

How this plays out across the ceramic range

The TSER-to-SIRR gap stays roughly constant across a product line but closes as you move up the tier ladder. Encore (carbon) at 35% VLT has TSER 40 and SIRR 48 — a narrow gap, because carbon has less infrared selectivity. Encore Supreme IR, the top ceramic tier, has TSER 57 and SIRR 93 at the same VLT — a 36-point gap, because the film is engineered to absorb aggressively in the narrow band SIRR measures.

This is the real reason to pay for ceramic. Not because the SIRR number is bigger (that part is a marketing effect), but because the TSER is bigger. The whole-spectrum rejection is what cools the cabin.

How to read any manufacturer's PDS

Every PDS from a legitimate manufacturer — Avery Dennison, 3M, Eastman (SunTek), XPEL, LLumar, Huper Optik, Solar Gard, Madico, Rayno — publishes the same core columns. Reading one correctly comes down to four questions:

1. Which row is my shade? Specs vary a lot across VLTs. “Up to 65% TSER” usually describes the darkest shade in the family; the one you actually install may be 10–20 points lower.
2. Which rejection column is the headline citing? Look for the full label — “TSER”, “Infrared Energy Rejection” or “Selective Infrared Rejection”. A table that uses only one acronym without defining it is a signal to be careful.
3. What glass was it tested on? NFRC methodology on 1/4" clear glass is the industry standard. If a PDS does not state the test substrate, the numbers are not comparable to other manufacturers' figures.
4. Is the UV figure above 99%? For any reputable film it should be. UV below 99% is a flag that the sheet is for a low-end film.

Everything else — TSHT (total solar heat transmitted), glare reduction, visible light reflected — is useful but secondary. If you can answer those four questions, you can hold your own with any shop.