Polyester (PET, typically hardcoated MacDermid Autotex AM or DuPont Mylar A) wins for embossed keys above 250,000 actuations, abrasion-prone surfaces, chemical wipe-down, and outdoor exposure. Polycarbonate (PC, typically Covestro Makrolon DE 1-1 or SABIC Lexan 8010MC) wins for indoor consumer products needing deep emboss above 0.8 mm, wide optical windows, and lowest BOM cost. The decision matrix in §5 covers seven priority cases.
- 1. Quick Verdict — At a Glance
- 2. Side-by-Side Material Specifications
- 3. Where Polyester Wins
- 3.1 Embossed Keys Above 250,000 Actuations
- 3.2 Abrasion-Prone Surfaces and Chemical Wipe-Down
- 3.3 Outdoor and UV Exposure
- 4. Where Polycarbonate Wins
- 4.1 Deep Embossing Above 0.8 mm
- 4.2 Wide Optical Windows for Displays and Backlighting
- 4.3 Lower BOM Cost for Indoor Consumer Products
- 5. Decision Matrix — Which to Specify
- 7. Methodology and Disclosure
A graphic overlay is the thin printed film that sits on top of a membrane switch or control panel — the user-facing surface that carries legends, key shapes, and dead-front windows. Two polymer families dominate the supply chain: polyester (PET) and polycarbonate (PC). Both bond to identical adhesives, accept identical screen and digital print processes, and meet the same UL flammability ratings. They do not, however, behave the same way once installed. The wrong choice fails in service; the right one runs for the equipment’s design life. Compare both materials across eight engineering dimensions, named test methods, and a decision matrix engineers can use during design review.
1. Quick Verdict — At a Glance
| Dimension | PET (polyester) | PC (polycarbonate) | Tie |
|---|---|---|---|
| Abrasion / scratch resistance (Taber CS-10F) | ✓ | ||
| Flex-cycle endurance (≥1,000,000 actuations) | ✓ | ||
| Chemical resistance (IPA, MEK, cleaners) | ✓ | ||
| Optical clarity for wide dead-front windows | ✓ | ||
| Embossing depth and sharpness | ✓ | ||
| Material + printing cost per m² | ✓ | ||
| UV / outdoor weathering (1,000 h QUV) | ✓ | ||
| Stock-gauge availability and lead time | ✓ |
Across eight dimensions, polyester takes four, polycarbonate takes three, and lead time is a wash. The win-loss split flips for indoor consumer products under 100,000 actuations, where polycarbonate’s lower cost and superior emboss usually outweigh polyester’s abrasion advantage.
2. Side-by-Side Material Specifications
The values below come from public technical data sheets — DuPont Teijin Films Mylar A, MacDermid Autotype Autotex AM-V, Covestro Makrolon DE 1-1, and SABIC Lexan 8010MC. Where the original TDS cites a specific ASTM or ISO test method, the method number is shown in parentheses so the value is independently verifiable.
| Spec | PET (Mylar A / Autotex AM) | PC (Makrolon DE 1-1 / Lexan 8010MC) |
|---|---|---|
| Polymer family | Biaxially oriented PET | Cast or extruded polycarbonate |
| Tensile modulus | 4.0 GPa (ASTM D882) | 2.3 GPa (ASTM D638) |
| Tensile strength | 200 MPa | 65 MPa |
| Elongation at break | 110% | 100–110% |
| Density | 1.40 g/cm³ | 1.20 g/cm³ |
| Continuous-use temp (max) | 150°C | 115–135°C |
| Total light transmission (clear) | 89% (ASTM D1003) | 89% (ASTM D1003) |
| Haze (velvet/matte) | 8–12% | 10–25% |
| Pencil hardness (hardcoat side) | 3H–4H (ASTM D3363) | F–HB; 2H with hardcoat |
| Taber abrasion (CS-10F, 500 g) | ≥250 cycles to wear-through (Autotex AM) | 50–100 cycles |
| Chemical resistance (IPA, MEK, ethanol) | Excellent on hardcoat | Fair on IPA; crazes with MEK/aromatic |
| UV weathering (ASTM G154) | Excellent — hardcoat survives 1,000 h+ | Fair — yellows without UV-stabilized topcoat |
| Flex endurance | 1,000,000+ actuations | 100,000–500,000 actuations |
| Practical emboss depth | 0.3–0.8 mm | 0.8–2.0 mm |
| Common stock gauges | 0.125, 0.175, 0.250 mm | 0.125, 0.175, 0.250, 0.500 mm |
| Flammability (typical grade) | UL 94 V-2; V-0 available | UL 94 V-2 to V-0 (e.g. Lexan 8010MC V-2) |
| Cost index (per m², 0.175 mm) | 1.0× (reference) | 0.70–0.85× |
Four numbers in the table drive most engineering decisions. Tensile modulus of 4.0 GPa for PET against 2.3 GPa for PC explains why PET resists flex fatigue better — a stiffer film distributes actuation load away from the key edge, where stress concentrates. The Taber CS-10F result, 250-plus cycles for hardcoated Autotex AM versus 50–100 cycles for unprotected PC, predicts which surface still reads legibly after three years of glove abrasion. The 150°C upper-service temperature for PET versus 115–135°C for PC matters in under-hood automotive and industrial-oven control panels. And the 0.70–0.85× cost ratio for PC is what closes most cost-down decisions on indoor white-goods.
For the spacer and mounting layers beneath the overlay, the adhesive selection logic is covered separately in JASPER’s [adhesive selection guide](/blog/choose-membrane-switch-adhesive/). Adhesive chemistry is identical for both substrates — 3M 467MP, 468MP, and 9472LE bond equally to PET and PC — so the overlay material decision is independent of adhesive choice.
3. Where Polyester Wins
Polyester takes the lead in four scenarios that share one trait: the overlay must survive mechanical or chemical stress that polycarbonate’s softer surface cannot.
3.1 Embossed Keys Above 250,000 Actuations
Hardcoated PET overlays routinely pass 1,000,000-actuation life tests with no measurable wear on the emboss radius. MacDermid Autotex AM specifies a typical service life of 1 million-plus cycles when laminated over standard membrane switch stack-ups. Polycarbonate, lacking the inherent flex modulus of biaxially oriented PET, typically fatigues between 100,000 and 500,000 cycles — the emboss flattens, key feel degrades, and the hardcoat (if applied) crazes at the dome perimeter. For medical devices and industrial HMIs rated for a 7-to-10-year service life, PET is the default.
3.2 Abrasion-Prone Surfaces and Chemical Wipe-Down
Hospital keypads see daily wipe-down with isopropyl alcohol, accelerated hydrogen peroxide, or quaternary-ammonium disinfectants. Food-prep equipment in commercial kitchens sees caustic cleaners and high-pressure hot water. Hardcoated PET surfaces tolerate these chemistries without crazing or surface haze; the Autotex AM TDS lists 50-plus chemicals against which the hardcoat retains pencil hardness and gloss. Polycarbonate without a hardcoat will craze under MEK, acetone, or aromatic solvents within seconds, and IPA exposure over 500-plus cycles produces a fine micro-crack pattern visible against backlighting.
3.3 Outdoor and UV Exposure
Agricultural equipment, marine controls, fuel dispensers, and outdoor kiosks face 1,000-plus hours of accumulated UV-A and UV-B exposure per year. Autotex AM hardcoated PET survives 1,000 hours of QUV testing per ASTM G154 cycle 1 with no significant change in haze, color, or gloss. Polycarbonate without a UV-stabilized topcoat yellows visibly after 200–400 hours of accelerated weathering. For applications where the harsh-environment trade-off drives the decision, the [harsh-environment selection guide](/resources/pet-vs-polycarbonate-harsh-environments/) walks through outdoor, chemical, and thermal-cycle priority cases in more depth.
4. Where Polycarbonate Wins
Polycarbonate’s three advantages all trace back to its lower tensile modulus and lower material cost. The same softness that hurts it on abrasion makes it the better choice for deep emboss, large optical windows, and cost-sensitive indoor builds.
4.1 Deep Embossing Above 0.8 mm
Cast polycarbonate is the easier polymer to form into deep, sharply defined key profiles. Practical emboss depths reach 2.0 mm on standard 0.250 mm PC film, against 0.8 mm maximum on the same gauge of PET. The lower elastic modulus of PC (2.3 GPa versus 4.0 GPa) means the film can be pressed into a tool cavity with less force and less risk of cracking at the radius. For large-format remote controls and industrial pendants with prominent tactile keys, PC delivers crisper key shapes and a more pronounced “click” feel.
4.2 Wide Optical Windows for Displays and Backlighting
Polycarbonate offers slightly lower haze than equivalent-gauge PET in clear-window configurations, and its lower birefringence reduces interference patterns visible through polarized LCD displays. For dead-front designs where a 50 mm × 80 mm window must reveal a TFT or graphic LCD when backlit, polycarbonate yields a cleaner visual through both the printed dead-front mask and the clear window. Both materials hit 89% total light transmission per ASTM D1003, but PC’s optical character is closer to the cast-acrylic look users expect on consumer electronics.
4.3 Lower BOM Cost for Indoor Consumer Products
For 0.175 mm film, polycarbonate runs 70–85% of polyester’s per-m² cost. On a high-volume indoor consumer keypad — microwave control panels, washer/dryer interfaces, indoor thermostats — that gap closes the business case on the cheaper substrate. The 100,000-to-500,000-cycle flex life of PC is more than the actuation count most consumer appliances see across a 7-year design life (a microwave keypad averages 50,000 lifetime presses). When the abrasion environment is benign and the cycle budget fits, polycarbonate is the rational choice.
5. Decision Matrix — Which to Specify
| If priority is … | Pick |
|---|---|
| Over 1 million actuations on embossed keys | PET (Autotex AM/V or equivalent) |
| Wide dead-front window, indoor display application | PC (Makrolon DE 1-1 / Lexan 8010MC) |
| Indoor consumer product, lowest BOM cost | PC |
| Deep tactile emboss above 0.8 mm on large keys | PC |
| Outdoor / UV exposure / chemical wash-down | PET — see the [harsh-environment guide](/resources/pet-vs-polycarbonate-harsh-environments/) |
| Medical or food-prep with daily IPA / disinfectant wipe-down | PET (hardcoated) |
| Cost-sensitive prototype, fewer than 50,000 units, indoor | PC |
When the requirement set spans both columns — for example, a deep emboss and 1-million-cycle target on the same key — the answer is sometimes neither. Composite stacks (PC keytop laminated to PET base, or 3-ply Autoflex constructions) cover that gap but trade tooling cost and lead time. Discuss with the overlay fabricator before locking the substrate on the assembly drawing.
6. Frequently Asked Questions
What’s the difference between polyester and polycarbonate graphic overlays?
Polyester (PET) is a biaxially oriented film with tensile modulus near 4 GPa, high abrasion and chemical resistance, and continuous-use temperature up to 150°C. Polycarbonate (PC) is a cast or extruded film with tensile modulus near 2.3 GPa, easier deep embossing, lower cost, and continuous-use temperature up to 115–135°C. PET wins on durability; PC wins on emboss depth, optical character, and price.
Which lasts longer in indoor use, PET or PC overlay?
In a controlled indoor environment without chemical exposure, both materials reach the 7-to-10-year design-life mark used by most OEMs. The differentiator is actuation count. Hardcoated PET overlays survive 1,000,000-plus actuations; standard PC overlays fatigue between 100,000 and 500,000 actuations. For appliance keypads averaging 50,000 lifetime presses, PC is durable enough. For industrial HMIs or medical devices exceeding 250,000 presses, PET lasts longer.
Is polyester or polycarbonate better for embossed keys on a graphic overlay?
Polycarbonate is the better material for embossed keys whenever emboss depth exceeds 0.8 mm or the key shape has sharp radii — its lower elastic modulus accepts deeper forming without cracking. Polyester is the better choice when emboss depth stays under 0.8 mm and the application requires more than 250,000 actuations. Hardcoated PET retains key-edge definition under repeated press cycles where PC begins to flatten.
Can polycarbonate overlays be used outdoors?
Unmodified polycarbonate yellows under UV-B exposure within 200–400 hours of QUV weathering per ASTM G154. UV-stabilized PC grades extend that to 600–800 hours but still trail hardcoated PET, which survives 1,000-plus hours with no significant color shift. For seasonal outdoor use — patio heaters, garden equipment, RV controls — UV-stabilized PC is workable. For permanent outdoor installation, specify hardcoated PET.
Is hardcoated polyester always more expensive than polycarbonate?
For the most common 0.175 mm gauge, hardcoated PET runs at roughly 1.0× the cost index against 0.70–0.85× for PC. The ratio narrows for thinner gauges (0.125 mm) and for premium PC grades that include factory-applied hardcoat or anti-glare finishes. On a finished overlay basis including printing and die-cutting, the substrate cost is typically 20–35% of total — so the gross 15–30% material delta translates to a 4–10% finished-part delta.
What overlay material has the best optical clarity for LCD windows?
Both PET and PC reach 89% total light transmission per ASTM D1003 in clear gauges. Polycarbonate has slightly lower birefringence, which reduces interference patterns visible through polarized LCD or e-paper displays. For wide windows over a TFT display, PC is the more common specification. For small clear windows or icon backlighting where birefringence does not matter, PET works equally well and brings better surface durability.
Does PET or PC handle higher operating temperatures?
PET handles a wider temperature window. Biaxially oriented PET films from DuPont, Toray, and Toyobo are rated for continuous use to 150°C. Polycarbonate films from Covestro and SABIC are rated to 115–135°C depending on grade. For under-hood automotive, industrial-oven controls, or industrial drying-line HMIs running above 100°C, PET is the conservative substrate choice.
Which material is more chemically resistant to cleaning agents like isopropyl alcohol or MEK?
Hardcoated PET is the more chemically resistant overlay film. The Autotex AM chemical-resistance chart lists more than 50 chemicals, including 70% IPA, accelerated hydrogen peroxide, quaternary-ammonium disinfectants, and MEK, against which the hardcoat retains its 3H–4H pencil hardness. Polycarbonate crazes within seconds of MEK or acetone contact and develops micro-cracks under repeated IPA wipe-down after 500-plus cleaning cycles.
7. Methodology and Disclosure
This comparison sources mechanical, optical, and thermal values from public technical data sheets — DuPont Teijin Films Mylar® A, MacDermid Autotype Autotex® AM-V, Covestro Makrolon® DE 1-1, and SABIC Lexan® 8010MC — cross-referenced against the named ASTM and IEC test methods. Cost-index values are an aggregated 2025 quotation average from three film distributors serving North America. Numbers are at-time-of-writing; verify against current TDS before locking a production specification.
Disclosure: This material comparison was authored by JASPER Electronics, a Shenzhen-based membrane switch and graphic overlay manufacturer. The technical analysis is supplier-neutral and applies to any overlay fabricator.
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