PETG Plastic FAQ — Clarity, Temperature, Thermoforming & Safety
Common questions about PETG (glycol-modified polyethylene terephthalate), answered for engineers, fabricators, and buyers. For the complete material overview, see the PETG material hub.
At a glance:
- PETG is amorphous, optically clear — not the same as semi-crystalline PET-P (Ertalyte)
- FDA 21 CFR 177.1630 compliant for food contact
- Thermoforms at 280–340°F oven temperature
- Continuous use limit: ~140°F (60°C)
- Impact resistance: 3–4× higher than acrylic
- Bonds with MEK or THF-based solvent cement
Q1: What is the difference between PETG and PET?
The abbreviation "PET" covers a family of related polyethylene terephthalate polymers that include several commercially distinct materials:
PETG is glycol-modified PET — amorphous, optically clear, thermoformable. It is used for displays, packaging, and machine guards. The glycol modification (CHDM co-monomer) prevents crystallization, giving it optical clarity.
PET-P (Ertalyte) is semi-crystalline PET with high molecular weight, used for precision machined bearings, wear components, and food-zone parts. It is opaque and not thermoformable.
Bottle-grade PET is the amorphous-to-crystalline PET used for beverage bottles — different molecular weight and processing history than either PETG or PET-P.
These are three distinct materials that happen to share the PET parent polymer. For engineering purposes, they are not interchangeable. See the PET vs PETG comparison.
Q2: Is PETG food safe?
Yes. Standard clear PETG complies with FDA 21 CFR 177.1630, which covers polyethylene terephthalate resins for food-contact use. This applies to:
- Direct food contact in packaging (trays, clamshells, blister packs)
- Food-zone equipment covers and display panels
- Food service containers and food preparation equipment covers
Request a Certificate of Conformance from your supplier confirming the specific lot meets 21 CFR 177.1630 for regulated food-contact applications.
Colored, UV-stabilized, or anti-static PETG grades need individual confirmation — the additives must also be FDA-approved. Details at PETG FDA compliance.
Q3: What temperature can PETG withstand?
Continuous service: ~140°F (60°C). Heat deflection temperature at 264 psi: 155°F (68°C). Glass transition (Tg): ~176°F (80°C).
In practice, PETG parts in direct sunlight through glass, near heat lamps, or in hot shipping containers can easily exceed 140°F and permanently distort. For applications near heat sources, specify polycarbonate (240°F) or acrylic (165°F) instead.
PETG is not autoclavable and is not suitable for dishwasher temperatures above 130°F.
Q4: What temperature is required to thermoform PETG?
Oven air temperature for thermoforming: 280–340°F (138–171°C). Sheet surface temperature at forming: approximately 240–280°F (115–138°C).
PETG's wide forming window makes it more forgiving than acrylic during thermoforming — slight under- or over-heating produces acceptable parts across a broader range. Pre-dry sheet at 140–160°F for 2–4 hours to prevent surface blistering from moisture. Full thermoforming guidance is in the PETG machining and fabrication guide.
Q5: How does PETG compare to acrylic for machine guards?
The critical difference is impact resistance:
- PETG notched Izod: 1.5–2.0 ft·lb/in
- Acrylic notched Izod: 0.3–0.4 ft·lb/in
PETG is approximately 4–6× tougher than acrylic. For machine guards where the occasional chip, tool drop, or operator contact will occur, PETG provides substantially better protection and does not shatter like acrylic. Acrylic guards crack at drill holes and corners under repeated stress — PETG absorbs this stress without fracturing.
Where scratch resistance is the priority (and impact is not a concern), acrylic's harder surface (Rockwell M94 vs PETG R106) is an advantage. See PETG vs acrylic for the full comparison.
Q6: Can PETG be bonded with solvent cement?
Yes — PETG is one of the easiest clear plastics to solvent-cement. MEK (methyl ethyl ketone) and THF (tetrahydrofuran) are the standard bonding solvents. Products like Weld-On 4 and equivalent formulations work well.
Apply with a needle applicator to the joint surface, press parts together, and allow 30–60 seconds of contact with light pressure. Full cure takes 24 hours. PETG solvent-cemented joints achieve joint strengths typically 50–70% of the base material tensile strength.
Unlike polycarbonate (which requires specialized adhesives or is difficult to solvent-bond), PETG solvent-bonds rapidly and reliably.
Q7: Does PETG scratch easily?
More easily than acrylic, less than polycarbonate. On the Rockwell scale, PETG (R106) is softer than acrylic (M94 — note the different scale; M values are generally higher hardness than equivalent R values), harder than polycarbonate (M70).
In practical display and guard applications, PETG accumulates light scratches faster than acrylic over time. For display applications where pristine optical appearance after extended use is critical, consider acrylic. PETG is acceptable for most machine guard and industrial display applications where periodic replacement is anticipated.
Scratch-resistant hard coatings are available on some PETG sheet grades from specialty suppliers.
Q8: Is PETG UV resistant?
Moderately. Standard PETG yellows gradually under direct UV exposure — starting after 6–12 months of direct outdoor exposure. For outdoor applications, specify UV-stabilized PETG (UV absorber additives) for extended service life, or switch to UV-stabilized acrylic for the best long-term outdoor performance.
Indoor applications near UV sterilization lamps (germicidal UV-C at 254 nm) also cause yellowing. If UV exposure is present, specify UV-stabilized grade or use a different clear plastic for those zones.
Q9: What sizes does PETG sheet come in?
Standard PETG sheet is stocked in:
- Sizes: 48" × 96" (primary), 24" × 48", 36" × 48"
- Thicknesses: 0.030" through 0.500" (and up to 1.0" for some applications)
For the complete size table and tolerances, see the PETG sheet page and PETG specifications.
Q10: Can PETG be printed on or painted?
Yes:
- UV flatbed printing: Direct UV inkjet printing on PETG sheet is standard practice in the sign industry; no primer required for most UV-cure inks
- Screen printing: PETG accepts screen-print inks formulated for PET and PETG substrates
- Painting: Use inks and paints formulated for flexible/clear substrates; solvent-based paints may craze PETG — test before production
- Laser marking: CO₂ laser engraves/marks PETG cleanly; laser cutting produces clean edges
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