If you have ever tried to compare two window films, you know the datasheets look like alphabet soup. This guide decodes every important number on a typical spec sheet, in plain English, with realistic ranges for each.
The six numbers that actually matter
| Spec | Meaning | Typical range |
|---|---|---|
| VLT | Visible Light Transmission — % of visible light passing through. Lower = darker. | 5% (limo) to 90% (clear) |
| VLR / VLR-Ext | Visible Light Reflectance (exterior) — how much light reflects off the window. Regulated in most states. | 5% (non-reflective) to 25%+ (mirrored) |
| TSER | Total Solar Energy Rejected — overall heat rejection across UV + visible + infrared. The headline comfort number. | 15% (basic dyed) to 70% (premium ceramic) |
| UVR | UV Rejection — % of ultraviolet light blocked. Highest health value. | 99%+ on almost every modern film |
| IRR | Infrared Rejection — the invisible heat wavelengths. Marketed heavily by ceramic brands. | 30% to 97%+ (narrow-band IRR) |
| SHGC | Solar Heat Gain Coefficient — similar to TSER but used in building-code contexts. | 0.3 (great) to 0.7 (weak) |
The two specs that control legality
VLT — your state’s minimum
VLT is the only number most state tint laws regulate. Check your state VLT minimum on the state index or the state comparison, then pick a film with a VLT above that number after factory-glass stacking. See VLT explained.
VLR — your state’s reflectivity cap
Most states cap exterior reflectivity at 20–25%. A film with VLR above that cap is illegal even if its VLT is compliant. Metallic films are the usual offenders. See reflectivity rules.
The specs that control comfort
TSER — the "hot cabin" number
TSER is the single most useful comfort number. A film with high TSER at your required VLT keeps the cabin cool. See best tint for heat rejection for benchmarks.
Good TSER thresholds: below 30% is basic dyed, 30–45% is carbon, 45–65% is ceramic, 65%+ is premium nano-ceramic.
IRR — marketing favorite, but context-dependent
Some manufacturers publish "IRR" numbers measured in a narrow band (900–1000 nm) that make films look spectacular (97%). This is honest but misleading — total solar infrared spans a much wider band. Trust TSER over IRR for real-world heat rejection.
UVR — the one easy spec
Virtually every modern automotive film blocks 99%+ of UV. This is the single most health-impactful stat; almost any film does the job.
A real-world comparison
Same VLT, same state-legal appearance — but Film B rejects twice as much total heat. That is the value of reading spec sheets.
| Spec | Film A (basic dyed) | Film B (nano-ceramic) |
|---|---|---|
| VLT | 35% | 35% |
| VLR (ext) | 5% | 7% |
| UVR | 99% | 99.9% |
| IRR | 18% | 92% (narrow-band) |
| TSER | 27% | 58% |
Spec sheet decoded: every acronym that matters
The full alphabet of tint specs
| Acronym | Stands for | Units | What it means |
|---|---|---|---|
| VLT | Visible Light Transmission | % | Light passing through (the legal number) |
| VLR | Visible Light Reflectance (exterior) | % | Light bouncing off outside (reflectivity cap) |
| VLR-i | VLR interior | % | Light bouncing back inside the cabin |
| UVR | Ultraviolet Rejection | % | UVA+UVB blocked (target 99%+) |
| IRR | Infrared Rejection | % | IR blocked (predicts felt heat) |
| TSER | Total Solar Energy Rejected | % | Full spectrum weighted (industry standard) |
| SHGC | Solar Heat Gain Coefficient | 0–1 | Energy through window (lower is cooler) |
| Tts | Total solar transmittance | % | How much solar gets through (inverse of TSER-ish) |
| Glare reduction | Compared to untinted | % | Marketing number; rarely standardised |
| SPF | Sun Protection Factor | number | Some films marketed with UPF 1000+ |
| Mil | Film thickness | thousandths | Standard auto film: 1.5–2 mil |
How to compare two films with confidence
When comparing spec sheets from two manufacturers, the numbers to align on — in priority order — are:
- 1. TSER at your intended VLT. This is the single most predictive number for cabin comfort. Higher = cooler.
- 2. IRR at your VLT. Confirms the film performs across the heat-relevant band, not just on paper TSER.
- 3. UVR. Should be 99%+ on any film you consider.
- 4. VLR (exterior reflectance). Must be below your state's reflectivity cap.
- 5. Warranty terms. Lifetime transferable > lifetime > 10-year > shorter.
- 6. Price. Usually the last factor, because per-year cost of a premium film is often lower than a budget film after replacement cycles.
How the industry measures these numbers
All reputable spec sheets are measured using NFRC (National Fenestration Rating Council) or ASTM E308 methodologies. The test setup:
- A solar simulator lamp emits a calibrated standard solar spectrum onto the film.
- Spectrophotometers measure transmitted and reflected light across the UV (280–380 nm), visible (380–780 nm), and IR (780–2500 nm) bands.
- Integration against the standard solar spectrum produces the weighted specs (TSER, UVR, IRR).
- Temperature-controlled test chamber to avoid cold/hot film skewing the measurements.
How to read a window tint spec sheet — FAQ
What is more important: VLT or TSER?
VLT determines whether the film is legal in your state. TSER determines how cool the cabin stays. You need both: legal VLT + highest TSER your budget allows at that VLT.
Why do some films advertise 97% IRR but low TSER?
IRR published in a narrow infrared band can be very high while total solar rejection (TSER, across all wavelengths) is mid-range. TSER is the honest comfort metric.
Is UVR really 99% on every film?
On virtually every modern aftermarket automotive film, yes. UV blocking is essentially solved; the differentiation is heat rejection and color stability.
How we verified this guide
- Primary sources only. VLT limits, windshield rules, and medical exemption procedures cited in this guide are verified against each state’s statute, administrative code, or DMV publication. See our sources & methodology.
- Annual re-review. Every guide is re-read against current state law at least once a year. This page was last reviewed on January 15, 2026.
- No affiliate influence. Our rankings, recommendations, and ticket-fighting advice are never paid. See our editorial policy.
- Not legal or medical advice. Enforcement is fact-specific; always verify with your local DMV, your state statute, or a licensed attorney before acting. See the legal disclaimer and medical disclaimer.
- Report an error. Spot something wrong or outdated? Contact our editors — we publish corrections quickly and note them in our next review cycle.