PETG — the complete guide
PETG is the workhorse of functional 3D printing — tougher than PLA, easier than ABS, food-safe (with caveats), and UV-stable enough for outdoor use. It also strings like nothing else and sticks to PEI sheets so well it can tear them. This guide covers every setting that matters and the two big tricks (glue stick as a release agent, dry before printing) that make PETG predictable.
Nozzle 230 °C, bed 75 °C, fan 30–50%, glue stick on PEI as a release agent (or use textured PEI). Dry the filament at 65 °C for 6 hours before every long print. Use for outdoor parts, mechanical brackets, food storage, water bottles, and anything PLA can't handle. Don't use for fine miniatures (PLA is better) or for anything that will see >75 °C continuous heat.
What PETG is
PETG is polyethylene terephthalate with added glycol (the "G") that prevents the brittleness of pure PET. The same plastic family as water bottles, with extruder-friendly modifications. It's slightly less stiff than PLA, much tougher (won't snap), and survives outdoors for years.
Recommended print settings
| Setting | Range | Notes |
|---|---|---|
| Nozzle temperature | 225–245 °C | 230 is a good starting point. Lower if stringing, higher for strength. |
| First-layer temperature | 240 °C | +5 to +10 °C above print temp. |
| Bed temperature | 70–85 °C | 75 is sweet spot; warmer for big parts. |
| Print speed | 40–80 mm/s | PETG flows slower than PLA — 60 is realistic on a stock hotend. |
| Volumetric flow | 8–12 mm³/s (standard); 18 mm³/s (Bambu high-flow) | Below PLA on the same hotend. |
| Part cooling fan | 30–50% | Higher than ABS, lower than PLA. 100% causes layer separation. |
| Retraction (direct drive) | 1.0–3.0 mm at 25 mm/s | More than PLA; less than Bowden. |
| Retraction (Bowden) | 4–7 mm at 25 mm/s | The stringiest filament — tune carefully. |
| Layer height | 0.12–0.28 mm | 0.20 is sweet spot. |
| Bed surface | Textured PEI (no adhesive) OR smooth PEI + glue stick (as release) | Smooth PEI without glue causes sheet damage on removal. |
The stringing problem
PETG strings even with perfect retraction. Strategies that actually help:
- Dry the filament first. Wet PETG strings no matter what. 65 °C, 6 hours.
- Lower nozzle temperature in 5 °C steps until under-extrusion appears, then back up 5.
- Enable retraction wipe (1–2 mm). The nozzle drags ooze onto the wall on retract.
- Enable coasting (0.2 mm). Stops extrusion before the line ends so the pressure equalises.
- Combing enabled, Z-hop disabled. Z-hop drags PETG strings.
- Lower travel acceleration if your machine has it set above 5,000 mm/s² — sudden direction changes shake ooze loose.
See the full stringing and oozing article for the exhaustive list.
The over-adhesion problem (PETG on PEI)
PETG bonds chemically to PEI on hot beds. The bond is often stronger than the PEI sheet itself, so removing the print rips the coating. The standard fix:
- Apply a thin layer of glue stick (Pritt, Magigoo) before each print. Acts as a release film — PETG bonds to glue, not PEI.
- Or use textured PEI (powder-coat) instead of smooth PEI — texture mechanically interlocks without the chemical bond.
- Let the bed cool to 40 °C before removing the print. The PETG contracts more than the PEI and pops off.
- Never force a hot PETG print off PEI — you will damage the sheet.
Strengths
- Tough: won't snap under impact; bends instead.
- UV stable: outdoor parts survive years (vs PLA's months).
- Water resistant: doesn't absorb water from the environment in finished prints; good for outdoor brackets, planters.
- Food contact: PETG is FDA-approved for food contact (but FDM layer lines harbor bacteria — not dishwasher safe for repeated food contact).
- Heat resistant: Tg ~80 °C — usable in cars (interior) and warm environments.
- Slight flex: 5–7% elongation at break vs PLA's 1–3%. Snap-fits live longer.
- Layer adhesion: excellent — PETG layers fuse strongly; isotropic strength.
Weaknesses
- Strings badly: requires more tuning than PLA.
- Hygroscopic: absorbs moisture from air in days, not weeks.
- Soft on cooling fans: too much cooling = layer separation.
- Bonds to PEI: see above.
- Glues poorly: only specific epoxies and PETG cement work. CA glue is mediocre.
- Hot-end residue: tends to ooze stringy gunk around the nozzle; clean regularly.
- Slightly heavier: 1.27 g/cm³ vs PLA's 1.24.
Mechanical properties (typical)
| Property | PETG | PLA (for comparison) |
|---|---|---|
| Tensile strength | 45–55 MPa | 50–65 MPa |
| Flexural strength | 60–80 MPa | 80–110 MPa |
| Impact (Izod, notched) | 5–10 kJ/m² | 3–5 kJ/m² |
| Elongation at break | 5–7% | 1–3% |
| HDT (heat deflection) | ~70 °C | ~55 °C |
| Density | 1.27 g/cm³ | 1.24 g/cm³ |
When to choose PETG
- Outdoor parts (planters, hose brackets, mailbox flags).
- Mechanical brackets and load-bearing fixtures.
- Snap-fit enclosures (won't crack under repeated open/close).
- Water bottles, food storage (single-use food contact OK).
- Living hinges (limited cycles, but workable).
- Anything PLA's heat resistance can't handle.
- Transparent prints (PETG transparent variants stay clearer than PLA over time).
Avoid for: fine miniatures (stringing leaves cleanup work), parts needing chemical resistance to acetone (use ABS), parts above 75 °C continuous (use ABS, ASA, PC), repeated dishwashing (use PP or commercial molded plastic).
Related articles
Sources & further reading
- Prusa Knowledge Base — PETG material guide
- Bambu Lab Wiki — Bambu PETG documentation
- Bambu Lab Wiki — Printing tips for transparent PETG