Polycarbonate vs PETG: Transparent Engineering Plastic vs Cost-Effective Sheet

Polycarbonate (PC) and PETG are the two most-used clear plastic sheet materials in fabrication, display, and protective cover applications — and they are genuinely different engineering choices despite both being amorphous, transparent thermoplastics. Polycarbonate is significantly stronger and tougher (it is used in bulletproof glazing), withstands higher service temperatures, and handles UV-stabilized outdoor exposure better. PETG is easier to thermoform at lower temperatures, less expensive, and more chemically resistant to certain cleaning solvents that attack polycarbonate. PETG is also easier to bond with common adhesives without the solvent-crazing risk that polycarbonate faces. For most retail display, sign, and light guard applications below 60°C, PETG is adequate and economical. For safety glazing, outdoor exposure, elevated temperature, or high-impact protection, polycarbonate justifies its premium.

TL;DR

• Impact resistance: Polycarbonate is dramatically tougher — 12–16 ft·lb/in notched Izod vs PETG's ~1.7 ft·lb/in. PC is used for bulletproof glazing; PETG is not.
• Temperature: Polycarbonate continuous service ~250°F (121°C); PETG ~158°F (70°C) — a major gap.
• Thermoforming: PETG thermoforms at lower temperatures (140–160°C) with a wider processing window; PC requires higher temperatures and tighter control.
• Chemical resistance: PETG resists many ketones and alcohols better; polycarbonate is attacked by acetone, MEK, and some adhesive solvents.
• UV resistance: Polycarbonate (UV-stabilized grades) better for outdoor applications; PETG yellows more readily.
• Cost: PETG significantly less expensive per square foot in sheet stock.
• Optical: Both are highly transparent; polycarbonate has slightly higher refractive index.

Chemistry & Origin

Polycarbonate is a polycarbonate ester of bisphenol A — an amorphous polymer with a rigid, bulky bisphenol A monomer linked through carbonate groups. The bisphenol A unit is the source of both PC's extraordinary impact resistance (the phenyl rings rotate and absorb energy on impact) and its notorious sensitivity to polar solvents (the carbonate linkage is susceptible to hydrolysis and solvent attack).

PETG is glycol-modified polyethylene terephthalate — the same polyester backbone as engineering PET but with cyclohexanedimethanol (CHDM) comonomer preventing crystallization. The resulting amorphous polyester is permanently clear, tougher at low temperature, and processable at lower temperatures than PET, but with reduced chemical resistance compared to semi-crystalline engineering PET.

Mechanical Properties

The impact resistance gap is extraordinary. Polycarbonate's notched Izod impact resistance of 12–16 ft·lb/in makes it among the toughest non-rubber materials known — it is the material of choice for bulletproof glazing, riot shields, and machine guards where impact protection is the primary design requirement. PETG's 1.7 ft·lb/in is respectable for a clear plastic and represents an improvement over acrylic (typically 0.3–0.5 ft·lb/in), but it is not in the same category as polycarbonate for impact-critical applications.

In tensile and flexural properties, the two materials are broadly similar — polycarbonate is modestly stiffer and stronger, but both are relatively soft compared to engineering resins like acetal or PEEK. For transparent structural applications, polycarbonate's impact dominance is usually the decisive factor.

Thermal Properties

The 90°F continuous service temperature gap (121°C PC vs 70°C PETG) is consequential in applications near heat sources, in automotive interiors, or in equipment that may see elevated ambient temperatures:

• PETG at 70°C is suitable for most indoor retail, display, and signage applications.
• Polycarbonate at 121°C covers automotive interior panels, instrument covers, lighting applications near LED/incandescent sources, and electronics housings that see self-heating.
• Neither material is suitable for sustained service above 130°C — above that, PEEK, Ultem, or glass-reinforced thermosets are required.

Thermoforming behavior differs significantly: PETG has a wide, forgiving thermoforming window at 140–160°C, making it the preferred material for vacuum-forming, drape-forming, and shop-bending operations. Polycarbonate requires higher temperatures (175–205°C) and more precise temperature control to thermoform without stress-whitening or cracking.

Chemical Resistance

Both materials have notable solvent vulnerabilities:

Polycarbonate is attacked by: acetone, MEK, ethyl acetate, chlorinated solvents, concentrated acids, and many adhesive solvents. Polycarbonate is particularly susceptible to stress-crazing — where surface stresses from machining or bending combine with solvent contact to produce cracking at much lower solvent concentrations than would affect an unstressed sample. Always anneal polycarbonate before cleaning with any solvent.

PETG is attacked by: ketones (acetone, MEK), chlorinated solvents, and concentrated mineral acids. However, PETG resists alcohols (isopropanol, ethanol) and some cleaning agents that attack polycarbonate. PETG also bonds more reliably with standard acrylic cements (methylene chloride-based) without the stress-craze risk present in polycarbonate.

For applications where chemical exposure is expected, verify resistance with the specific cleaning agent and grade before specifying either material.

UV Resistance and Outdoor Use

UV-stabilized polycarbonate is the preferred clear plastic for outdoor glazing, skylights, and greenhouse panels. Standard PC yellows under UV but UV-co-extruded grades provide 10+ year outdoor life with minimal color shift. Standard PETG yellows more rapidly under UV and is generally recommended only for indoor applications or short outdoor exposure periods.

Fabrication and Bonding

PETG is easier to work in a fabrication shop: lower thermoforming temperature, wider forming window, and good bondability with standard acrylic cements and CA adhesives. Polycarbonate requires more care: higher forming temperature, annealing to relieve machining stresses before solvent bonding, and solvent selection that avoids crazing. For custom fabricators without extensive plastics processing experience, PETG is a more forgiving material.

Cost & Availability

PETG sheet is a commodity item at competitive prices — often 30–50% less expensive than polycarbonate in equivalent thicknesses. Both are widely stocked in clear sheet from 0.030″ to 1.0″+. Polycarbonate is also available in UV-stabilized grades, tinted/colored, and anti-reflective coated; PETG offerings are primarily clear standard grades.

When to Choose Polycarbonate vs PETG

Choose Polycarbonate when:

• High-impact protection is required — machine guards, safety glazing, riot shields, bulletproof applications.
• Service temperature exceeds 70°C (158°F).
• UV-stabilized outdoor glazing is needed.
• Structural rigidity in a transparent panel application is required.

Choose PETG when:

• Application is indoor display cases, signage, light diffusers, or protective covers at ambient temperature.
• Easy thermoforming or vacuum forming is required.
• Lower cost is the priority and impact performance is moderate.
• Chemical resistance to isopropanol or common sanitizers is needed (PETG handles these better than PC in many cases).

More related guides

Applications

• Display and Signage
• Machine Guards
• Structural Glazing

Industries

• Retail / Display
• Automotive
• Electronics

Other comparisons

• Acrylic vs PETG
• PET vs PETG
• PEEK vs Ultem PEI

Spec sheets

• Polycarbonate hub
• PETG hub