There are many reasons why FDM users choose PETG (polyethylene terephthalate) as their 3D printing material. More substantial and impact resistant than PLA, this inexpensive thermoplastic offers a good level of flexibility and is suitable for mechanical parts. Other advantages of PETG include its good chemical and moisture resistance, as well as its natural transparency.

While PETG offers several advantages, it can also cause headaches for FDM users. Without proper preparation and calibration, PETG prints can exhibit a large amount of bleeding and stringing—an undesirable phenomenon where the printhead nozzle deposits hair-width strips of plastic as they travel from one part of the structure to another.

Stringing is a problem that often occurs in 3D printing when the 3D printer has to travel through empty space to get from one part of the print to another. During this process, thin strings of fibers sometimes form between the two sections. This can affect the print quality and finish of your 3D prints.

PETG is a great material that is a popular choice for 3D printing. It can withstand higher temperatures than PLA, has good adhesion, and is usually not too difficult to work with. Like any material, it also has its drawbacks.

PETG needs a high printing temperature and specific hardware requirements such as a heated pad and cover to print properly. It is also prone to problems such as threading, bubbles, and uneven extrusion. Most of these problems can be avoided using the correct print settings and following proper filament storage protocols. But before that, what is 3D printing?

What is 3D Printing?

3D printing, or additive manufacturing, is a process of creating three-dimensional objects by building them up layer by layer from a digital model. The digital model is created using an STL editor or any other software. Unlike traditional manufacturing methods that involve the removal of material to create complex shapes, 3D printing uses various materials and technologies to build precise structures from the ground up. This allows for an unprecedented level of customization and control in product design, opening up new possibilities for innovation across a wide range of sectors. And thanks to advances in technology and materials, 3D printing is becoming increasingly affordable and accessible, making it a valuable tool for both businesses and individual creators alike.

Ways to quickly fix the PETG Stringing

Maintain Nozzle Temperature

Getting the nozzle temperature right for your PETG filament is the first step to preventing PETG threading. This process may take some time to figure out. Running the extruder too hot will cause the filament to have too high a viscosity. This increases the flow of filament from your extruder, resulting in threading and drips as the nozzle travels from one part of the print to another.

A typical nozzle temperature range for printing with PETG filament is between 210°C and 250°C. However, this will vary depending on the brand of filament used and your 3D printer. Check the manufacturer’s recommended print temperature ranges to be sure. We recommend using a temperature tower to test print quality at 5-10°C intervals to determine which temperatures work best for your particular setup.

Always keep the filament dry

Moisture can cause threading regardless of the material. It creates tiny air bubbles in the filament, which burst when the material is heated. This cracking can cause the molten filament to escape, resulting in threading if the nozzle is in motion. As PETG is particularly prone to threading, it is necessary to keep PETG filament spools dry: by storing them in a closed container with a desiccant, placing them in a filament dryer, or gently heating them in an oven before printing.

Tune Retraction Speed

Your draw setting is another important factor in reducing PETG yarn in your 3D prints. Retraction speed refers to how quickly the extruder retracts the filament as it travels from one area to another. Slow retraction speed is a common cause of run-out and threading because the extruder does not retract fast enough to stop the filament flow.

A good starting speed for your pull is 25mm/s. However, the correct drag settings will vary from 3D printer to 3D printer. You will need to experiment a bit until you find the correct settings for your machine. Use a test print where you increase the retraction speed by 2-5mm/s each time until you see enough improvement.

Maintain Travel Speed

If adjusting the pull setting alone does not resolve the threading, you may need to change the printhead feed speed. Travel speed is the speed at which the hot end moves between two points without (intentionally) depositing material. If the printhead moves faster, there is less time for droplets to form or excess material to drip from the nozzle. Combining a higher travel speed with a slower print speed can also help reduce threading.

Maintain Nozzle Temperature

PETG extrusion requires a high-temperature nozzle to ensure good material flow and layer adhesion. MatterHackers recommends an extrusion temperature of around 245°C. Even if you are using a dual extruder 3D printer you need to nozzles of each of them.  However, higher temperatures and free-flowing material can lead to stringing. When using PETG, try reducing the print temperature in 5°C increments to see if threading can be reduced without reducing print quality and durability, clogging, or adversely affecting adhesion (first layer or otherwise). You can also try increasing the speed of the cooling fan to cool the PETG after it leaves the nozzle.  

Adjust Printing Setting

Print speed indicates how fast the 3D printer print head moves during printing. A lower print speed usually results in better print quality. The printer has enough time to push the material exactly where it needs to go. On the other hand, high print speeds make it difficult for a 3D printer to extrude and position the molten filament accurately.

However, if you have a problem with threading or PETG bubbles, increasing the print speed may help. This is because slow print speeds keep your extruder in the same place for longer, and your nozzle has more time for unwanted filament leaks. PETG filament usually has the best results when printing between 40-60mm/s. While you should test your settings until you find the perfect speed, print speed should not be your first concern for PETG threading problems. High print speed can help threading but can also cause other problems.