PET (polyethylene terephthalate) is an extremely popular thermoplastic polymer resin most commonly used as a material for plastic bottles and synthetic fibers.[1] And in a slightly modified form known as PETG or PET-G, it becomes an excellent 3D printing filament with good durability, impact resistance, chemical resistance, and layer adhesion.

Glycol modification — the chemical process that puts the “G” in PETG — helps to lower the melting point of the thermoplastic, which makes it easier to print. However, PETG users should familiarize themselves with the ideal printing temperature, print bed temperature, heated chamber temperature, and cooling settings for PETG before attempting to print with it.

This article goes over the key PETG temperature considerations, providing tips that will prevent warping, stringing, and other common printing issues.

Recommended reading: ABS print temperature considerations: Nozzle, bed, enclosure

Thermal properties of PETG

PETG is a modified form of PET. It is created when some ethylene glycol groups in PET are replaced with cyclohexanedimethanol (CHDM) groups.[2] Because CHDM has extra carbon atoms, it is less stable, which prevents crystallization and ultimately lowers the melting point of the plastic — without compromising its other material characteristics.

In this modified form, PETG is slightly easier to manipulate using thermal manufacturing techniques like FDM 3D printing, injection molding, and thermoforming.

PETG has many advantages, but a high level of temperature resistance is not one of them. In fact, with a glass transition temperature of around 80 °C, PETG is only slightly better than PLA at maintaining rigidity at higher temperatures. In other words, you don’t want to leave PETG parts in very warm environments, as they might soften up and lose their functionality. That being said, it will take some serious heat for PETG to turn fully liquid: the plastic has a melting point of around 210 °C.

So 3D printed PETG parts are only fractionally more heat-resistant than PLA parts. However, this doesn’t mean that PETG filament can be printed at very low temperatures like PLA. In fact, the ideal printing temperature for PETG is closer to what you would use for ABS, a plastic with excellent thermal resistance. The following section explains how to adjust your 3D printer’s temperature settings to get good results when using PETG.

PETG temperature settings

3D printing software applications usually have printing profiles for different 3D printing materials, including PETG, that contain preset parameters suitable for the particular 3D printer filament. Nonetheless, it is useful to become familiar with the ideal PETG temperature settings in order to understand exactly what your 3D printer is doing (and to be able to fine-tune the settings whenever print quality issues occur).

PETG 3D printing temperature

Using the right 3D printer nozzle temperature is vital for getting good prints. Too low a temperature will cause under-extrusion and potential jamming, while too high can cause oozing and stringing, with filament leaking onto areas it isn’t supposed to go.

The ideal PETG hot end temperature (nozzle temperature) is 220–260 °C, with the exact sweet spot varying depending on the 3D printer hardware, filament type, and requirements for the specific print job. Prusa recommends a printing temperature of 230 °C for the first layer of the print and 240 °C for the remainder.[3]

For high-strength parts, a temperature nearer 260 °C may be preferable, because the extra heat will improve bonding between layers. Lower temperatures may be suitable for visual parts where surface finish is important.

Recommended reading: Nozzle diameter and layer height explained

Using a higher temperature can improve inter-layer adhesion 

Bed temperature

A heated build plate can prevent warping and help with bed adhesion and part removal. PETG filament prints well with a heated print bed set to a temperature near the glass transition temperature of the material. However, a heated bed is not absolutely necessary as long as a suitable build surface is used, such as powder-coated PEI sheet, blue painter’s tape, or another surface coated with glue stick or hairspray.

A heated bed temperature of 65–90 °C should lead to good bed adhesion of PETG parts to the build surface and minimize the chances of warping.

Heated chamber

Heated enclosures (chambers) are a feature of some 3D printers, helping maintain an even temperature around the part during the FDM 3D printing process. Heated chambers are particularly useful for high-temperature materials like ABS.

A heated chamber is not required for PETG, since the material is not prone to warping or shrinkage.

Cooling

If a printed layer remains soft and malleable for too long after being extruded, it can cause warping of the part. A good way to prevent such warping is to use a 3D printer’s cooling fan, which helps the printed sections to harden faster. It is especially useful when printing overhangs.

PETG users should deploy their cooling fan at a fan speed of 30–60%, bearing in mind that a higher fan speed will also have the negative effect of reducing adhesion between layers.

The printer's cooling fan can be used to prevent deformation

Other PETG printing tips

To get the most out of a spool of PETG filament and make high-quality parts, you’ll have to do more than adjust temperature settings.

An important early step to take is to properly prepare the print surface on the build plate. PETG offers excellent first-layer adhesion, but this means the plastic can also become overly stuck to the build surface. Because of this, it can be helpful to use a textured build surface such as powder-coated PEI sheet to facilitate part removal.[4] Alternatively, you can use a more common surface like blue painter’s tape or a separating agent like glue stick on whatever surface you currently use.

Another key part of PETG printing is retraction settings. When the hot end of the extruder heats up filament, it can make the material overly runny, which causes blobs to form in the nozzle and allows excess material to leak out onto the printed part. This is called oozing, and when the escaped material forms a weblike pattern over the part, it is called stringing. By increasing retraction speed and retraction distance, these PETG printing problems can be avoided.

Retraction settings are key to preventing stringing

Finally, PETG likes to be printed at a slow print speed. Around 60 mm/s at most will provide good results. On the other hand, a fast travel speed should be utilized — making the hot end move quickly when it is not depositing material — to prevent oozing and stringing.

For a more comprehensive list of PETG printing tips, see our PETG print settings article.

Conclusion

PETG is not a difficult material to print, but it requires a different set of printing parameters than PLA or ABS. And among the most important of those parameters are temperature settings like nozzle temp, bed temp, and cooling fan speed.

By tailoring these settings to meet PETG’s unique needs, FDM users should have no problem achieving high-quality prints with this versatile printing material.

References

[1] The Science Behind PET [Internet]. PET Resin Association. 2015 [cited 2022Mar20]. Available from: http://www.petresin.org/science_behindpet.asp

[2] Feng YC, Zhao H, Hao TH, Hu GH, Jiang T, Zhang QC. Effects of poly (cyclohexanedimethylene terephthalate) on microstructures, crystallization behavior and properties of the poly (ester ether) elastomers. Materials. 2017 Jul;10(7):694.

[3] PETG [Internet]. Prusa Knowledge Base. 2020 [cited 2022Mar20]. Available from: https://help.prusa3d.com/en/article/petg_2059

[4] How to Succeed with LayerLock Powder Coated PEI Build Plates [Internet]. MatterHackers. 2019 [cited 2022Mar20]. Available from: https://www.matterhackers.com/articles/how-to-succeed-with-layerlock-powder-coated-pei-build-plates