Optically Clear Polyester Film: A Practical Guide to Specifications, Selection and Sourcing
Optically clear polyester film is biaxially oriented polyethylene terephthalate (PET) made to transmit light with very little scatter. It sits behind many everyday products: touch-panel overlays, optical adhesive carriers, medical device windows and premium label face stocks. Buyers often ask for "clear PET" and then discover that two films with the same headline transmittance can behave very differently in a laminate.
What "Optically Clear" Actually Means
Clarity is defined by two measurements, both covered by ASTM D1003 (Haze and Luminous Transmittance of Transparent Plastics):
- Light transmittance is the share of visible light that passes through the film. Our standard grades reach 89–92%.
- Haze is the share of transmitted light scattered more than 2.5 degrees away from the incident beam. Low haze keeps text and images sharp. Our clear film holds haze below 1.0%.
One point that datasheets rarely explain is that transmittance has a physical ceiling. PET has a refractive index of roughly 1.64, so each surface reflects about 6% of incident light. With two surfaces, even a flawless film cannot pass much more than 90%. If a supplier claims 93% or more, check whether the figure was measured with an anti-reflective coating or as a laminate. For bare film, the useful comparison is haze at equal thickness, not a difference of one point in transmittance.
Standard Technical Specifications
The values below are typical performance figures for Targanix optically clear polyester film. Each lot ships with a certificate of conformance, and you can see how rolls are inspected on our Quality Control page.
| Property | Test Method | Typical Value | Why It Matters |
|---|---|---|---|
| Light transmittance | ASTM D1003 | 89–92 % | Display brightness and image fidelity |
| Haze | ASTM D1003 | < 1.0 % | Sharpness of text and graphics |
| Thickness range | ASTM D374 | 12–250 µm | Stiffness, handling and stack height |
| Tensile strength (MD) | ASTM D882 | 150–220 MPa | Web handling and die-cut durability |
| Elongation at break | ASTM D882 | 80–120 % | Resistance to tearing during converting |
| Shrinkage (150 °C, 30 min) | ASTM D1204 | < 1.5 % | Registration accuracy after drying or curing |
| Melting point | DSC | ~255 °C | Upper limit for processing |
| Surface energy (after corona) | ASTM D2578 | ≥ 42 mN/m | Ink and adhesive wet-out |
Tensile strength, thickness range and operating temperature (−40 to +150 °C) are what separate PET from commodity films. Standard rolls are available up to 1600 mm wide, which suits wide-web coating and lamination lines.
Four Technical Issues That Cause Most Failures
1. Rainbow patterns under polarizers
Biaxial stretching gives PET a degree of birefringence, meaning light is retarded differently along different axes. On a plain surface this is invisible. Behind polarized sunglasses or over an LCD polarizer, it can appear as colored fringes. If your product is a display cover, tell your supplier early. Film grade and orientation balance should be chosen for the application, not just for haze.
2. Haze that develops after heating
Uncoated PET contains small amounts of cyclic oligomers. When film is held at high temperature, these can migrate to the surface and crystallize, raising haze. For processes that expose film to sustained heat, such as adhesive curing or sterilization, request a heat-stable grade or a primer layer, and test haze after the thermal cycle, not just on delivery.
3. Poor adhesion and coating defects
Untreated PET is chemically inert, so inks and adhesives may not bond reliably. Corona treatment raises surface energy to 42 mN/m or higher, and an adhesive-ready primer improves bonding with optical clear adhesives and pressure-sensitive adhesives. Surface energy fades with storage time, so schedule converting soon after treatment and keep film sealed and dry in the meantime. For adhesive systems, see our adhesive range.
4. Static, dust and scratches
Clear film attracts particles, and a single trapped speck can ruin an optical laminate. Anti-static and hard-coat options reduce the risk. For cleanroom assembly, choose an anti-static coating and check that packaging keeps rolls sealed until they reach the line.
Choosing a Surface Treatment or Coating
The right coating depends on the end-use environment. Coatings are applied using our in-house coating technology to keep coverage uniform.
| Treatment | Main Benefit | Typical Use | Sides |
|---|---|---|---|
| Corona | Better ink and adhesive anchorage | Printing, label lamination | One or two |
| Hard-coat | Scratch and abrasion resistance | Touch panels, screen protectors | One |
| Anti-glare | Fewer surface reflections | Outdoor displays, instrument panels | One |
| Anti-fog | Prevents condensation distortion | Cold-chain and medical packaging | One |
| Anti-static | Reduces dust attraction | Electronics, clean-room processing | One or two |
| Adhesive-ready primer | Stronger bonding to OCA and PSA | Optical adhesive carriers | One or two |
| Matte finish | Diffused light, less gloss | Nameplates, graphic overlays | One |
Two coatings interact with clarity in ways that surprise buyers. An anti-glare or matte finish deliberately increases haze, so it cannot be combined with an ultra-low-haze requirement. A hard-coat, by contrast, usually preserves clarity when applied evenly.
PET, PE or PP: Which Clear Film Fits?
PET is not always the right choice. If your label needs to squeeze or conform to a curved container, a softer film may work better. The comparison below uses the figures from our film label material page.
| Attribute | Clear PET | PE | PP |
|---|---|---|---|
| Haze | < 1.0 % | 2–5 % | 1–3 % |
| Tensile strength | 150–220 MPa | 20–40 MPa | 30–60 MPa |
| Temperature limit | Up to +150 °C | Up to +80 °C | Up to +100 °C |
| Dimensional stability | Excellent | Moderate | Good |
| Best for | Displays, medical, optical | Flexible packaging, general labels | Food labels, squeezable packs |
As a rule of thumb, choose PET when you need rigidity, heat tolerance or precise registration. Choose PE or PP when flexibility and conformability matter more than absolute clarity.
Where Optically Clear Polyester Film Is Used
- Electronics and displays: touch-panel overlays, sensor covers and carrier films for optical adhesives.
- Automotive and aerospace: heads-up display protection, dashboard laminates and sensor cover films.
- Medical and diagnostics: device display covers, instrument screens and packaging windows that must tolerate sterilization.
- Printing and packaging: nameplates, graphic overlays, transparent windows and security label substrates.
See how these materials serve different sectors on our Industries page. If the film will become a pressure-sensitive label, browse our self-adhesive materials as well.
A Checklist for Requesting a Quote
Sending complete information up front shortens the technical review and avoids sample rounds that miss the target. Include:
- Thickness and roll width, including core size and maximum roll diameter.
- Required optical limits, stated as maximum haze and minimum transmittance.
- Coating or treatment needs, and which side each applies to.
- Process conditions: peak temperature, dwell time, solvents, and any sterilization method.
- The adhesive or ink system that will contact the film.
- Annual volume and delivery destination.
Our process runs in four stages: inquiry, technical review, pre-production sample with test reports, and bulk production shipped with a certificate of conformance. Send your specifications through the contact page to start. Datasheets and further documents are on the Download page, and after-sales help is under Service.
Frequently Asked Questions
Is higher transmittance always better?
Not necessarily. Bare PET tops out near 90% because of surface reflection. Low haze and consistent gauge usually decide real-world clarity more than small differences in transmittance.
Can clear PET be printed directly?
Yes, after corona or primer treatment. Confirm ink compatibility with a sample, since surface energy declines with storage time.
Does the film yellow over time?
Standard PET can shift color under prolonged UV exposure. For long-term outdoor use, ask about UV-stabilized options and confirm suitability with a test.
Can I get custom widths and gauges?
Yes. Custom thickness, width and coatings are available on request within the ranges shown above.
