PETG is a glycol-modified variant of PET (Polyethylene Terephthalate) and the most popular material in the PET family of plastics. The glycol in PETG offers improved printability and toughness compared to other PET copolyesters making it the most suitable variant for 3D printing. Due to the benefits and popularity of PETG, it is uncommon to print pure PET filaments.

PETG offers improved mechanical and thermal properties when compared to PLA, while maintaining excellent printability and reliability. Although not a direct replacement for ABS, PETG is a great choice for users who experience difficulty printing ABS due to warping or cracking and require improved mechanical properties to PLA with excellent dimensional stability.

PETG exhibits a low chemical resistance and moderate temperature resistance, softening at 80°C (Glass Transition and Vicat temperature).

Printer Setup

Requirements

An enclosed professional 3D printer is not required but will be beneficial when printing PETG. We recommend only printing with a quality PETG filament.

Minimum Extruder Temperature - 230°C (±15°C) is required (Correct temperature will vary on your printer) (245°C recommended, lower temperature for bridging.
Heated Bed - Required, 75° - 85°C.
Enclosure - Not required (Open door if printing on enclosure printer)
Part Cooling Fan - OFF or LOW (OFF for functional parts (better layer adhesion), low for improved bridging and appearance).
Feeding / Spooling - No specific requirements.

Some 3D printing slicers (software) have a pre-configured PETG or CPE profile. The accuracy of this profile may vary depending on if you are using 1st or 3rd party filament. If a PETG or CPE profile is not available we recommend duplicating a PLA or ABS profile to start with and making necessary adjustments covered in this article.

Bed Surface

Printing with the right bed surface is very important when printing PETG. For PETG we recommend first trying the surface your 3D printer was designed to use.

Bed Leveling & Nozzle Height 

It is important when printing PETG that your first layer adheres to the printing bed.

• Your bed must be properly leveled.
• Your nozzle height must be set correctly. (distance between the nozzle and bed)

Since PETG will require a heated bed when printing, preheat the heated bed (75 - 85°C) before calibrating your nozzle height or leveling.

The ideal gap between the nozzle and bed is typically a distance of 0.1mm, this is the thickness of two pieces of paper. PETG sticks to itself very well and because of this, can stick to the nozzle during printing. To prevent this it can be beneficial to print with a slightly larger nozzle gap than you usually would.

When changing between bed surfaces, it is important to adjust the nozzle height again to compensate for the added thickness of the bed surface.

Filament Storage

When not in use PETG should be stored away from sunlight and in a resealable bag with desiccant.

Like many other plastics, PETG is a highly hygroscopic material, absorbing moisture from its surrounding environment. When the filament passes through the hot end the moisture rapidly expands creating bubbles in between layers, poor layer adhesion, inconsistent extrusion due to material expansion and thus poor surface quality.

PETG will typically absorb moisture over a period of months however in environments with high humidity (evaporative air-conditioning) this process can take days.

Preventing Moisture Absorption:
It is important to store and print your PETG materials in their optimum environment (below 20% humidity) to prevent moisture absorption, as excessive drying will degrade the filament. We recommend storing filaments in a resealable bag with desiccant when not in use and we recommend using a filament dry box when printing. 

Printer Settings

Nozzle Temperature

PETG has a moderate printing temperature, typically printing between 230°C - 250°C. (245°C for functional parts)
Of course the printing temperature range of PETG filaments will vary depending on which printer and filament brand you use.

PETG is more susceptible to oozing and sticking to the nozzle, these characteristics can be reduced with the correct nozzle temperature. Higher extrusion temperatures will typically result in better flow and layer adhesion, ideal for printing mechanical parts whereas lower extrusion temperatures allow the plastic to cool and solidify faster, beneficial for users interested in overhang surface quality and easier support removal. 

When starting we recommend trying a temperature right in the middle of the manufacturer’s suggested settings. If the manufacturer recommends 230°C - 240°C, printing at 235°C is a good starting point. If your extruder can not reach the highest recommended temperature, try printing at the lower temperature. Based on the quality of the print we suggest adjusting ± 5°C at a time.

Bed Temperature

Printing PETG requires a heated bed at 75°C - 85°C.

We generally don't recommend heating your heated bed above the glass transition temperature of PETG (80°C ). 

Cooling

When printing PETG you can print with the part cooling fan ON or OFF. The best results will vary depending on your printer.

If you are interested in maximizing layer adhesion and strength, we recommend printing with the cooling fan OFF.

Printing with the cooling fan ON will improve surface quality and reduce stringing.

If you can control the power of your cooling fan, even setting the fan speed to 20% can help to improve the quality of overhangs and reduce sagging.

Troubleshooting

Poor surface quality

PETG should ideally print with a clean and smooth surface finish. Please consider these notes if the surface quality of your models is rough or textured.

Improving surface quality.

• We first suggest checking that your spool of PETG is dry. An easy way to test for moisture content in a spool of filament is to extrude the filament, if you hear a distinct popping sound your filament has likely absorbed moisture. As the filament is extruded, the moisture will expand and rupture in the filament creating a rough and inconsistent extrusion. Typically If you experience issues with moisture, printing with a dry box and applying preventative measures will be important to maintain the best printing results.
• If your extruder temperature or flow rate is too low during printing, the PETG filament won't extrude properly, leaving gaps within the model. Printing with the correct nozzle temperature will solve this issue.
• Too much friction on the filament feeding path can result in under extrusion. To reduce resistance on the filament you can move the spool holder closer to the 3D printer and check the curve of the filament guide tube is not too tight.
• If your extruder temperature is too high during printing the filament can sag when printing steep unsupported overhangs. We recommend printing with the cooling fan set to a LOW setting to achieve the best underside surface quality. Printing with a lower nozzle temperature can also improve overhang surface quality.
• If your nozzle is partially blocked the filament will have difficulty extruding. 
• Slowing down your printing speeds can help to minimize vibration, ensure consistent extrusion and improve printing quality. Our high quality profile for bowden system is around 45mm/s max speed printing speed, 60mm/s infill.
• Printing with the wrong retraction settings can negatively impact the quality of a 3D print. If the retraction distance is too high and the retraction speed is too slow, the nozzle won't be primed with enough material when the next layer starts, resulting in gaps. Temporarily turning off retraction settings is one way to see if retraction is causing gaps in the model. If the poor quality is related to retraction, printing with a lower retraction distance, faster retraction speed or turning off coasting may solve under extrusion when printing with retraction. If the retraction speed is too high, the feeding gear may grind the filament, causing a filament jam.
• If there are gaps in the top surface of your 3D print this is commonly referred to as pitting. Pitting can be related to temperature or moisture however generally occurs when the infil is to low to support the top layers of the 3D print. This can be solved by increasing the number of top layers on your model to match the layer height you are printing. 6 top layers with a 0.2mm layer height will result in a 1.2mm top surface thickness, the same number of top layers at 0.1mm layer height will only result in a 0.6mm top surface thickness. Printing with 12 top layers with a 0.1mm layer height will achieve the 1.2mm top surface thickness.

Cleaning a PETG Nozzle Blockage
If the nozzle is blocked with PETG one of the most successful solutions is to feed a tougher material like PC through the extruder / hot end. As polycarbonate is a considerably tough material, with assistance and a high nozzle temperature you can generally purge and remove the clogged plastic.

If you cannot remove the blockage of PETG plastic from the nozzle, we recommend swapping to a spare nozzle.

Sticking to nozzle

During printing the viscosity of PETG is similar to some glues. This characteristic can cause filament to build up on the nozzle during printing and impact print quality.

Solutions to preventing PETG sticking to nozzle.

• Adjusting how your first layer prints can help to prevent filament from sticking to the nozzle. Some filaments are best printed when the first layer is 'squished' into the bed, but printing PETG this way will cause plastic to stick to the nozzle. Increasing the gap between the nozzle and bed can help solve this issue.
• Printing with the right flow of material is critical to preventing this behavior, this can be controlled by adjusting the nozzle temperature or cooling fan.
• Increasing retraction and the travel speed can help reduce oozing which can stick to the nozzle. For PETG, it could be beneficial to reduce the retraction speed.
• Some 3D printers will perform a movement known as a Z-hop. The bed will lower (or nozzle will raise) by a small amount to prevent the nozzle from dragging on the surface. This can be beneficial when printing delicate structures. Printing PETG with z-hop enabled can create wisps that the nozzle will pickup. So it always best to z-hop disabled when possible.

Heat Creep

What is heat creep?

Jamming can occur when heat creeps up the extruder to the extruder gear and softens the filament too early. This can cause many problems including the filament chewing out instead of gripping and feeding through the hot end.

Heat creep affects lower temperature materials like PETG due to their low softening temperature of 80°C and the issue is more prominent on enclosed high temperature 3D printers, some dual extruder printers where a section of filament sits idle for long times or cheap 3D printers with poorly designed extruders.

Solutions to preventing heat creep.

The first step is to make sure the extruder fan is cooling the extruder as intended. If the printer is enclosed, printing with all front doors and top hatches open may help to cool and prevent the filament from softening near the extruder gear. Printing on the lower end of the materials extrusion temperature can also help reduce heat creep in some cases.

Heat creep related jams may be more common when printing parts with retraction. The filament will feed past the extruder gear multiple times with each retraction, this makes it far easier for the extruder gear to ‘chew out’ the filament. Printing simple parts with little or no retraction are more likely to be successful as the filament will only be passing the gear once.

Stringing / Oozing

PETG based materials can flow more easily than other materials leaving behind wisps of plastic during travel movements. By controlling the travel and flow behavior in the slicing software we can minimize and prevent oozing and stringing.

Minimizing and preventing stringing.

• Printing with a cooler nozzle temperature will in many cases help to reduce unwanted oozing as the plastic will flow and solidify at a different rate.
• By increasing the retraction length or retraction speed in your slicer settings, the extruder will withdraw a short distance filament from the nozzle, helping to prevent oozing when the extruder travels between points.
• Increasing travel speed can reduce the 'idle' time of the nozzle and minimize the opportunity for stringing to occur.
• Advanced slicer settings like coasting can be turned on to effectively reduce stringing.
• Printing PETG with z-hop enabled can sometimes create wisps that the nozzle will pickup, printing with this feature disabled may reduce stringing.
• If the spool has absorbed moisture, the moisture will affect the flow rate and viscosity of the material causing unwanted stringing and wisps.

Warping

PETG materials can typically be printed easily on most machines with excellent dimensional stability. In some cases it is possible for PETG materials to warp or lift, lets look at what can cause PETG prints to warp or lift off the bed.

Preventing warping.

• The most common reason for PETG parts to warp or lift during the print is due to insufficient bed adhesion or an incorrect nozzle height. If the first layer of extruded plastic is not sticking to the bed, a small amount of residual stress will be enough to lift the part off the bed. It is important to ensure your nozzle height and bed is leveled correctly and that you are using the correct printing surfaces for PETG. (Smooth PEI depend to warp very easily on larger object, we suggest textured/frosted flex PEI)
• Drafts, cool air from air conditioners and low environmental temperatures in winter can cause the material to behave differently and will print with more internal stress. An enclosure with a closed front door can help to maintain the right printing environment.
• Not every heated bed is made equal, some designs heat from the center, reaching lower temperatures around the edges of the build platform. Preheating can help to even out the temperature across the print bed.
• Printing with the heated bed at 80°C will help to heat up the surrounding environment and improve bed adhesion and printing consistency. Depending on the thickness of the bed, some printers will accurately heat the bed to 80°C but in reality the surface of the bed may only be reaching 70°C, with some machines it may be required to set the bed to 80-90°C.

Poor Layer Adhesion

Causes and steps to improve poor layer adhesion.

• If the filament is under-extruding during printing there will be inconsistencies and gaps between the layer, compromising  mechanical strength and layer adhesion. It is important to ensure you are printing the PETG filament at the right nozzle temperature to ensure consistent flow and to minimize drag or tension which may prevent the filament from feeding. Calibrate flow on filament.
• Printing with the cooling fan ON can negatively impact inter-layer adhesion of PETG. Printing with a LOW setting like 20% or OFF setting can significantly improve inter-layer adhesion.
• If your model is printed with a lot of internal stress, the inter-layer performance of your model will be compromised. We recommend following our tips in relation to cracking.
• Poor layer adhesion can also be caused when printing with PETG that has been spoiled with moisture. When the filament passes through the hot end, the moisture erupts creating bubbles in the extruded plastic, compromising  the parts mechanical properties. If a spool of filament has absorbed moisture, it can be dried however it is important to store the PETG correctly to prevent this issue from occurring.

Poor Bed Adhesion

• Please account for an additional 0.02mm to 0.06mm margin when printing with PETG. Unlike PLA and ABS, PETG does not adhere well to the print bed. Neglecting this may lead to the nozzle gliding over freshly printed material, resulting in material build-up that can manifest as wispy strings or clumps. These accumulations can solidify, increasing the risk of nozzle collisions with the print and potentially causing minor imperfections on the surface of your print.

Parts difficult to remove from platform

To print a successful print excellent adhesion between your first layer and the the bed is critical, but in some cases it can be difficult to remove models if your adhesion is too good.

Causes and steps to improve print removal experience

• Some users prefer to apply Magigoo Original to their print bed. With Magigoo parts will self release when the bed cools down, making print removal easy.
• For Frosted/texture flex PEI, wait until bed is cooled and flex build plate to remove the part.
• Some print surfaces specifically manufactured for PETG materials are designed to maintain adhesion with the part when the bed is heated and self-release when the part is cool. Try removing the models when the heated bed is hot or cold to see what method best suits your printing surface.

If you are printing on glass (without Magigoo), please always remove the part when the glass bed is HOT.

• Your heated bed may be operating too hot or your nozzle temperature may be too close to the bed. You can try making slight adjustments to the heated bed temperature or nozzle height if this improves your user experience. Of course this is a fine balance as adhesion between the print and platform is important to achieve successful prints.

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