PETG stringing is a common problem caused by liquid plastic still oozing out of the print nozzle as it travels between points.
PETG filament is notorious for stringing issues because of the high temperature required for 3D printing PETG is responsible for stringing.
Luckily we can reduce stringing by adjusting our slicer settings. We can remove stringing from your 3D prints with enough 3D printer calibration and patience.
How to Prevent PETG Stringing
There are several ways to reduce PETG stringing. From adjusting slicer settings, cleaning your nozzle, and drying your filament, here’s how to prevent PETG stringing.
1. Enable Retraction Settings
Retraction is the process of the printer’s extruder pulling the filament back away from the nozzle when the nozzle is moving over an air gap. Retraction allows the printer to “suck in” the molten plastic before it can ooze out between movements.
If you’re struggling with stringing, enabling retraction should be your first step.
In Curas slicing software, the retraction section has two main settings; Retraction Speed and Retraction Distance.
The retraction speed refers to how quickly the extruder motor pulls the filament away from the nozzle when the nozzle is moving over an air gap.
You can reduce stringing by increasing the retraction speed. A faster speed quickly reduces pressure in the print head and prevents unwanted filament extraction.
When 3D printing PETG, we recommend a retraction speed between 25mm/s and 45mm/s.
I usually keep my restriction speed around 45mm/s on my Ender 3 V2 Pro and haven’t noticed any stringing on my PETG prints.
Retraction distance is the distance the filament will be pulled away from the nozzle. A 2-5 mm retraction distance is sufficient on most Bowden tube setups.
If you are using a direct drive extruder (without a Bowden tube), you will likely benefit from a low retraction speed (25-35mm/s) and a lower retraction distance (1-2mm). Direct drive extruders are more precise than the Bowden setups and don’t require as much retraction.
When adjusting the retraction settings, it’s best to change one setting at a time and monitor the results. You can print a retraction test print from Thingiverse to inspect how the changes impact PETG stringing.
It’s best to make small changes by first adjusting the retraction speed in 5mm/s increments and adjusting the retraction distance in 1mm increments.
Note: Don’t raise the retraction speed too much, or it could jam the printer nozzle.
Your 3D printer won’t always retract filament over small spaces. You can adjust the minimum distance required to enable retraction by changing the “minimum travel distance.”
By decreasing the minimum travel distance, you can tell your printer to enable retraction over smaller distances.
2. Decrease Print Temperature
One of the best ways to fix PETG stringing is to decrease your printer’s nozzle temperature.
A relatively high temperature produces a more liquid (or viscous) filament.
If your printer nozzle temperature is too hot, your filament may still ooze, even with the proper retraction settings.
PETG manufacturers recommend a nozzle temperature between 235°C and 250°C. You can find the manufactures recommendation on the filament roll.
The manufactures recommended printing temperature should serve as a guideline and may not be perfect. Factors like the ambient temperature, your 3D printer, and whether you use an enclosure affect the performance of the filament at different print temperatures.
If you want to reduce stringing, it’s best to calibrate your nozzle temperature by printing a temperature calibration block or temperature tower. The temperature tower is our preferred calibration method because it shows stringing and surface details in 5-10°C increments.
You may be unable to completely reduce stringing by adjusting the nozzle temperature. And you may need to accept some minor strings in your 3D prints. You don’t want to eliminate striking at the cost of other surface imperfections.
3. Increase Travel Speed
Opposite to print speed, travel speed is the speed at which the nozzle moves when it is not printing and is moving over an air gap.
A higher travel speed means your nozzle spends less time over an air gap. Increasing travel speed reduces PETG stringing because there’s less time for the filament to melt during transitions.
Further, having a high travel speed will mean that you will have a rapid acceleration of the part and will help break the plastics connection from the part.
Don’t be afraid to set your travel speed to ridiculously high values. We’ve had success setting the travel speed as high as 150mm/s. Other makers have gone as high as 200mm/s without any problems.
You can achieve higher travel speed on sturdy printers like a CoreXY 3D printer. Other open frame printers like the Ender 3 and Prusa i3 MK3S+ are limited to travel speeds of 100mm/s or less.
A high travel speed shouldn’t impact your print quality, aside from reducing PETG stringing.
Once the nozzle reaches the next point of the print, it rapidly decelerates to your regular print speed and continues its normal printing.
If your print has many gaps, the print head’s rapid accelerations and decelerations can produce vibrations. If your printer is sturdy, it shouldn’t impact the quality of your 3D printing.
But over time, the vibrations may loosen some of the screws on your printer. We encourage you to inspect your 3D printer periodically and tighten the mounting screws to keep your printer sturdy.
4. Adjust Printing Speed
Although travel speed is more important, adjusting your print speed can reduce PETG stringing. Generally, the slower the print, the more accurate it will be, as it will increase the time the printer has to lay down the plastic.
However, a higher print speed may reduce PETG stringing in your prints.
With a low print speed, the extruder moves slower, allowing more time for the plastic to ooze out of the nozzle. Fast print speeds purge the hot end from its excess pressure faster and help reduce extra plastic oozing out over the air gap.
Most filament rolls have a recommended print speed on the side of the filament roll. We recommend beginning with their recommendation and making adjustments in 5-10mm/s increments.
We’ve found the best results in 3D printing PETG with print speeds between 40-60 mm/s. Generally, it’s best not to print PETG above 60mm/s.
5. Dry Your Filament
If the above tips haven’t fixed PETG stringing, wet filament might be the cause.
PETG is hygroscopic, meaning it will absorb moisture from the air. Printing with “wet filament” can cause undesirable appearances in finished prints.
When the plastic gets heated up in the hot end, the moisture will evaporate and will cause pressure in the nozzle. The pressure will have nowhere to go other than out the nozzle tip.
Additionally, the steam may try to escape the print head. It can do so in a quick, violent “pop” that throws molten plastic onto your print.
All this to say, we don’t want to print with wet filament.
Even if you have all your retraction and speed settings dialed in perfectly, the pressure will want to exit the nozzle and will likely take some molten filament with it creating stringing, zits, and blobs.
You can check if your filament has absorbed moisture by using a set of calipers to precisely measure the diameter of the filament. 3D printing filaments are usually either 1.75mm or 2.85mm in diameter and generally have a tolerance listed on the side of the spool.
If your measured diameter is more significant than 1.75mm or 2.85mm plus the maximum tolerance, it is safe to say your filament is wet, and you should dry it before printing.
You can also check by running a print. You’ll know immediately if the filament is wet because the heated plastic will hiss and pop inside the print head.
If your filament has absorbed moisture, you can dry it or print with a new filament roll.
You can purchase a filament dryer or carefully dry the wet filament in a dehydrator or oven.
If you’re serious about getting high-quality prints, we recommend purchasing a filament dryer like the one below.
It’s important to store your filament in a moisture-free environment to prevent 3D printing filament from absorbing too much moisture.
6. Enable Coasting
When coasting is enabled, your printer will stop extruding shortly before the end of a print movement. The rest of the printing movement uses the molten plastic left in the print head.
Coasting helps to reduce pressure within the print head before it travels over an open area. When coasting is enabled, your printer is less likely to extrude melted filament.
Coasting is difficult to calibrate and is the last resort to fix PETG stringing.
If you’re still struggling after making the adjustments above, it’s worth trying. Fine-tuning the coasting distance is essential. Otherwise, you might find holes between layer lines or on the edges of your prints.
7. Enable Combing
Combing is a feature that calculates a travel path to limit how much time the extruder spends over empty spaces. Combing reduces stringing by restricting the nozzle’s time traveling over open spaces.
Enabling combing doesn’t eliminate stringing because it doesn’t directly affect filament extrusion. Instead, combing works to reduce the amount of stringing in your prints.
The downside to combing is that it can add to your overall print time.
If adjusting the settings above doesn’t reduce stringing in your 3D prints, you may want to try combing.
8. Use a Quality PETG Filament
If you want to achieve quality 3D prints, it’s best to stick with the best PETG filaments. Upgrading to a quality PETG filament can make a big difference in the quality of your PETG prints.
Reputable manufacturers use quality materials, equipment, and production techniques to ensure a better product with better tolerances.
You should only print with PETG filaments with a tolerance of +/-0.05mm. The tolerance means that the diameter of the filament may be 0.05mm thicker or thinner when measured at different points.
Smaller tolerances generally mean a higher quality filament. Lower-quality filaments have higher tolerances which can produce inconsistencies in your printing.
We recommend printing with Overture PETG, which has a +/- 0.03mm tolerance.
9. Clean the Nozzle
Dust, debris, and filament residue can accumulate within your nozzle. After using your printer for a long time, the accumulated residues can create surface defects such as strings.
It’s essential to clean your print nozzle periodically to remove dirt and filament residue from previous prints.
There are several ways to clean your 3D printer nozzle:
- Wipe the nozzle head: External dust and residue can impact print quality. It’s a good habit to wipe the printer nozzle after it has preheated. Tip: Be careful not to burn your fingers on the hot nozzle.
- Cleaning filament: Cleaning filament is a special kind of filament designed to clean the inside of the print head. Simply load the cleaning filament and heat the print head to the normal printing temperature, and it works to capture and remove debris and filament residue as it extrudes.
- Wire brush or needle: if you don’t have cleaning filament, you can insert a wire brush into the nozzle to remove dirt. You can also use a needle to remove chunks of printing material, but it isn’t as effective. Note: Be very careful when cleaning the print nozzle with a wire brush or needle. They can damage the nozzle and create printing issues down the line.
- Acetone: If you’re really struggling to clean the nozzle, an acetone bath can remove tricky contaminants.
How to Remove Strings From 3D Prints
Dealing with PETG stringing in your 3D prints isn’t fun.
You can remove most of the stringing by hand. But there will always be stubborn bumps and strings.
You can remove the residual strings with a heat gun or small torch to get a smooth surface finish.
Ensure you don’t keep the lighter in the same spot for long because the plastic may get soft, melt or even burn.
You should only use a heat gun, torch, or lighter in a well-ventilated outdoor space. Ensure you wear personal protective equipment, flame-resistant gloves, and a P100 respirator. Heated plastic can be toxic.
Does PETG Need More Retraction?
Yes, especially if you are comparing the retraction settings of PLA, PETG needs a higher retraction speed and distance.
Is PETG Hygroscopic?
Yes, PETG is hygroscopic and will begin to absorb moisture from the environment until it reaches its saturation limit.