If you have been shopping for window film, you have probably seen ads claiming "97% IR rejection" or "99% infrared rejection." These numbers sound impressive. But they are often misleading — and understanding why could save you from buying the wrong film.
What Is IR Rejection?
Infrared (IR) radiation is the portion of sunlight responsible for the heat you feel when sunlight hits your skin or passes through a window. IR makes up roughly 49–53% of the total solar energy that comes through your window.
IR rejection measures how much of that infrared portion a film blocks. A film that blocks 97% of IR sounds extremely effective — and it may be, for that specific slice of the solar spectrum. But here is the problem: IR is not the only source of solar heat gain.
What Is TSER?
TSER stands for Total Solar Energy Rejected. It measures how much of the entire solar energy spectrum — visible light, infrared, and ultraviolet — a film rejects. TSER is the number that tells you how much total heat your room will actually gain or lose after the film is installed.
TSER is calculated using the NFRC/ASHRAE methodology and accounts for all three components of solar radiation:
| Component | % of Solar Energy | Included in IR? | Included in TSER? |
|---|---|---|---|
| Visible Light (380–780nm) | ~43% | No | Yes |
| Near-Infrared (780–2500nm) | ~53% | Yes | Yes |
| Ultraviolet (280–380nm) | ~4% | No | Yes |
A film with 97% IR rejection might only have a TSER of 40–55% — because it is only blocking the infrared slice, not the visible light that also carries heat into your room.
Why Brands Advertise IR Instead of TSER
The marketing problem: IR rejection numbers are almost always higher than TSER numbers for the same film. A film with 55% TSER might have 85% IR rejection. Advertising "85% IR rejection" sounds better than "55% TSER" — even though TSER is the more complete and honest number.
This is not necessarily dishonest — IR rejection is a real measurement. But it is an incomplete measurement when used as the primary heat-rejection claim. Some brands lead with IR because their films perform well in the infrared range but less well overall. Others do it simply because the number is bigger and more impressive to consumers who do not know the difference.
A Real-World Example
Consider two films:
| Film | IR Rejection | TSER | What It Means |
|---|---|---|---|
| Film A | 97% | 42% | Blocks most infrared but lets significant visible-light heat through. Net heat reduction is moderate. |
| Film B | 72% | 71% | Lower IR number but blocks far more total solar energy. Your room will be significantly cooler. |
Film A would win in an IR-focused ad campaign. Film B would win in your living room on a Las Vegas summer afternoon.
What ASWF Reports — And Why It Matters
ASWF reports both IR rejection and TSER on their spec sheets — but TSER is the primary heat-performance metric used on this site. Every film page on seymourclearly.com shows the TSER number prominently, labeled as manufacturer-reported from the official ASWF spec sheet.
Our standard: Every number on this site is sourced from the manufacturer's spec sheet and labeled as manufacturer-reported. We do not inflate specs, and we do not lead with IR rejection to make films sound better than they are. TSER is the number that matters for heat reduction — and it is the number we show first.
The Bottom Line
When comparing window films, always ask for the TSER number. If a brand only gives you IR rejection and will not provide TSER, that is a red flag. TSER is the industry-standard metric used by NFRC, ASHRAE, and the DOE for evaluating window film performance. It is the only number that tells you how much total heat your room will actually gain or lose.
For reference, here are the TSER values for the highest-performing ASWF films we install:
| Film | TSER | VLT |
|---|---|---|
| ASWF Illusion™ | 85% | 7% |
| ASWF Reflection™ 20 | 84% | 14% |
| ASWF Sky™ 10 | 85% | 8% |
| ASWF Daydream™ 5 | 80% | 6% |
| ASWF Horizon™ 20 | 80% | 18% |
Not Sure Which Film Is Right for You?
Nicholas will assess your windows and sun exposure, then recommend the film that gives you the best real-world heat reduction for your situation.
Call (702) 418-7600 — Free Quote