PET or polyethylene terephthalate is one the world’s most widely used plastics. Found in synthetic textiles, bottles, and packaging, PET has many desirable characteristics, such as strength, transparency, and lightness.[1]

Because of these characteristics and others, PET has become a go-to material in FDM 3D printing. In filament form, PETG (glycol modified PET) offers some notable advantages over PLA, such as excellent layer adhesion, good impact resistance, and a low level of shrinkage. It’s affordable too: a spool of cheap PETG filament only costs about $5 more per kilogram than PLA from an equivalent filament brand.

Printing good PETG parts can be tricky, however. When melted, the plastic has a low level of viscosity, which — while great for fast extrusion — can cause issues like oozing and stringing. Furthermore, its excellent bed adhesion can be both a blessing and a curse, with parts sometimes remaining stuck to the print bed after printing.

With that in mind, it is essential to properly prepare your 3D printer when printing PETG. And while many slicers provide default settings for individual materials like PETG, it is beneficial to understand what these settings are achieving so that fine-tuning can be carried out to achieve even better prints. This article gives a rundown of the correct PETG printer settings for most situations — though different printers have their own unique requirements — in addition to general advice such as print bed preparation.

PET is used to make plastic bottles

Build surface & bed temperature

Compared to ABS and other low-adhesion materials, printing PETG can be a breeze. PETG will stick to most surfaces without too much trouble — in fact, steps should be taken to stop the material adhering too well and becoming stuck to the build plate.

Choosing the right build surface is important when dealing with PETG. Very smooth surfaces like a glass bed can lead to over-adhesion, and such surfaces should be coated with glue stick or hairspray — which can function as a separator rather than an adhesive — to prevent damage to the build and the print bed.[2] Blue painter’s tape is a suitable surface for most PETG prints. However, a better solution is to use a textured build surface such as a powder-coated PEI sheet. Bear in mind that a textured print surface will leave a shallow patterned imprint on the bottom of the part, but this is a small price to pay for easy part removal.

PETG prints best onto a heated print bed with a temperature of 65–90 °C. As a rule, if good first-layer adhesion can be achieved at the lower end of that range, then stick with that temperature.

Nozzle temperature

PETG usually prints best in the temperature range of 220–260 °C. 3D printer company Prusa suggests a printing temperature of 230 °C for the first layer and a slightly higher temperature of 240 °C for the rest of the build.[3] Filament company MatterHackers recommends 245 °C throughout.[4] If good results can be achieved at a lower temperature, stick with it, as a high temperature can lead to issues with bridging and overhangs.

Bed leveling and nozzle calibration is another important step when adjusting PETG print settings. The distance between nozzle and print bed should be greater than it is with PLA, ideally around 0.1 mm. This is due to the low viscosity of PETG: as the material flows freely, it can “drop” from the nozzle onto the bed without having to be forced vigorously.

Print speed

Print speed is one of the simpler PETG print settings to configure. In general, the material is best printed at a slow speed, ideally around 60 mm/s. This leads to improved bonding and cooling, and consequently better print quality. Some users report good results with faster speeds for the first layers.

Perhaps more important, however, is the travel speed: the speed at which the printhead moves along the X and Y axes when it isn’t depositing material. Travel speed should be fast — around double the print speed, i.e. 120 mm/s — in order to mitigate the potentially damaging effects of oozing and stringing: if the hot end moves slowly across the print area, it has more time to drip excess material onto the part, causing imperfections and potentially leading to print failure.

Retraction

Adjusting retraction settings can prevent PETG stringing

Most PETG users would agree that the single biggest disadvantage of the printing material is its tendency toward oozing (when material seeps from the nozzle) and stringing (when the seeping material forms a weblike mess across the part) — undesirable phenomena caused by the low viscosity of the plastic.

The best way to counter oozing and stringing is to adjust retraction settings. Retraction is a feature of FDM extruders wherein the nozzle pulls back a small amount of filament before it travels along the X and Y axes. By doing so, the printer can prevent unwanted leakage of the material and improve print quality. If stringing occurs during PETG printing, the following retraction print settings should be adjusted:

• Set retraction distance to 3–7 mm, increasing it in increments of 1 mm until the stringing stops. The distance should be slightly higher for Bowden extruders than direct drive extruders.

• Set retraction speed to around 20 mm/s, increasing it in increments of 5 mm/s if necessary.

• Reduce or remove the minimum travel distance for retraction.

• Disable any vertical lift feature (such Z-Hop in Cura, a popular slicer).

Fan & cooling

When adjusting PETG print settings, the 3D printer’s fan should be taken into account. In general, cooling a part during printing — bringing the temperature down to below the material’s glass transition temperature — can reduce issues like warping and sinking, leading to better parts.

Overall, using PETG can be advantageous because it exhibits a very low level of shrinkage as it cools, which means that parts — even very large ones — tend to maintain their shape as they are being printed. This means the plastic is less dependent on the printer’s cooling fan than a material like PLA; some users choose not to use their fan at all when using PETG 3D printing filament, though this might be considered risky.

For most prints, using a fan speed of 30–60% should suffice to prevent issues like oozing and stringing. However, only use the fan after the first few layers of the printing, as this will help to prevent warping, and remember that too high a fan speed will prevent interlayer bonding and result in a weaker PETG part.

Conclusion

PETG is a valuable 3D printing material due to its strength, impact resistance, affordability, and resilience against shrinkage and warping. With careful consideration of build surface, retraction settings, and other printing parameters, it is possible to achieve high-quality PETG prints on most FDM printers.

3D printer users should stick closely to the following PETG print settings:

• Use a textured build surface

• Use a heated bed with a temperature of 65–90 °C

• Use a printing temperature of 220–260 °C

• Keep nozzle height at around 0.1 mm

• Print slowly at around 60 mm/s

• Use a fast travel speed of around 120 mm/s

• Increase retraction distance and speed

• Use a moderate fan speed

By doing so, printed PETG parts should have good layer adhesion and a good surface finish while exhibiting minimal oozing or stringing.

References

[1] The Science Behind PET [Internet]. PET Resin Association. 2015 [cited 2022Mar14]. Available from: http://www.petresin.org/science_behindpet.asp

[2] How to Get Perfect PETG Prints on Ender-3: Correct Settings [Internet]. Creality. 2020 [cited 2022Mar14]. Available from: https://www.creality.com/blog-detail/how-to-get-perfect-petg-prints-on-creality-ender-3

[3] PETG [Internet]. Prusa Knowledge Base. 2020 [cited 2022Mar14]. Available from: https://help.prusa3d.com/en/article/petg_2059

[4] Black MH Build Series PETG Filament [Internet]. MatterHackers. 2016 [cited 2022Mar14]. Available from: https://www.matterhackers.com/store/l/petg-black-high-strength-filament-1.75mm/sk/M3MY2VQG