Window Film Glossary

Window film spec sheets are full of acronyms. Here is what they mean, in plain English. For how the film types differ in practice, see types of window film; to compare real specs, see our window film brands & specs.

Performance numbers

Visible Light Transmission (VLT)

The percentage of visible light that passes through. Lower VLT means darker film: 5% is "limo" dark, 70% is nearly clear. State tint laws are written in VLT.

Net VLT

The VLT of film and glass together, which is what a police meter reads. Car glass is not perfectly clear (usually 70–85% VLT), so a quick estimate is glass VLT × film VLT: a 35% film on 80% glass gives about 28%. Allow for this when choosing a legal shade; see tint laws by state.

Total Solar Energy Rejected (TSER)

The share of the sun's total energy (visible light, infrared and UV) that the film and glass keep out. Higher is better. It is the most useful single number for comparing heat rejection.

Infrared (IR) rejection

How much infrared light the film blocks. It is often quoted for a narrow band where films perform best, so it runs higher than TSER. Compare TSER across brands when you can.

UV rejection

The share of ultraviolet light blocked. Most quality films block 99% or more, which protects skin and slows fading of interiors.

Solar Heat Gain Coefficient (SHGC)

The fraction of solar heat that gets through the window and film, from 0 to 1. Lower means less heat gain. Common on architectural spec sheets.

Shading coefficient

An older measure of solar heat gain compared with plain clear glass. Lower is better. SHGC has largely replaced it.

U-value

How easily heat passes through the window and film. Lower means better insulation, which matters most in cold climates.

Emissivity

How much heat a surface radiates. Low-emissivity (low-E) films reflect heat back into the room in winter, lowering the U-value.

Visible light reflectance

How much visible light the film reflects, inside and out. High reflectance gives a mirrored look; some states limit it on cars.

Glare reduction

How much the film cuts visible light compared with clear glass. It tracks closely with VLT.

Solar absorptance

The share of solar energy the film and glass absorb as heat. High absorption on some glass can cause thermal stress, which is why film makers publish glass compatibility charts.

Types of film

Dyed film

Polyester film colored with dye. Inexpensive and non-reflective, but it rejects less heat and can fade over time.

Carbon film

Uses carbon particles instead of dye. A matte look, better heat rejection than dyed film, and it doesn't fade.

Metalized film

Has a thin metal layer that reflects heat. Durable and effective, but shinier, and it can interfere with phone and GPS signals in cars.

Hybrid film

Combines a dyed layer with a thin metal layer, for less reflection than fully metalized film.

Ceramic film

Uses non-metallic ceramic particles to block infrared. High heat rejection even in light shades, no signal interference, and no mirror look.

Spectrally selective film

Film that lets most visible light through while blocking infrared, so it keeps rooms cooler without looking dark.

Low-E film

Architectural film with a low-emissivity coating that also insulates in winter.

Safety and security film

Thicker film that holds broken glass together after an impact, accident or break-in attempt.

Decorative film

Frosted, patterned, colored or textured film used for privacy and design rather than heat control.

Static cling film

Film with no adhesive that clings to glass and can be removed and reused. See static cling vs adhesive film.

Paint protection film (PPF)

Thick, clear urethane film that protects car paint from chips and scratches. Also called a clear bra. See paint protection.

Wrap film (cast and calendered)

Colored vinyl that changes a vehicle's look. Cast films are thinner and conform better to curves; calendered films are cheaper and suit flatter surfaces.

How film is made

Polyester (PET)

The clear, strong plastic that almost all window film is built on.

Sputtering

A vacuum process that knocks metal atoms off a target so they settle on the film in a very thin, even layer. Used for high-end metalized and low-E films.

Vapor deposition

A vacuum process that heats metal until it evaporates and condenses on the film. Faster and cheaper than sputtering, with less control over the layer.

Scratch-resistant coating (hard coat)

A hard top layer that protects the film surface from everyday scratches.

Pressure-sensitive adhesive

The adhesive on most window film. It bonds as the film is squeegeed onto wet glass and cures over days to weeks.

Mil

A thousandth of an inch, used for film thickness. Car tint is typically 1.5–2 mil; security films run 4 to 15 mil or more.