PETG can be quite tricky to 3D print, especially when the PETG filament becomes brittle or weak. I decided to write an article detailing how to fix PETG filament that becomes weak to help users out.
To fix PETG filament or 3D prints that become brittle, first make sure you are using the right printing temperature, since low temperatures can cause bad layer adhesion. It’s important to also dry your PETG filament if it has been left out without being stored in an airtight container. Use zero to low fan speeds.
This is the simple answer but there are more details you’ll want to know so keep reading for more.
Why Does PETG Filament Get Brittle?
PETG becomes brittle due to a number of issues during printing, one is poor bed adhesion, and another is improper printing temperature for the bed and the hotend. Also, when e-step calibrations are not done for your 3D printer or you are experiencing a clogged nozzle, your 3D prints can become brittle.
Also, high fan speed which cools down so quickly can cause the filament to be brittle, and using a filament that has been exposed to moisture.
How to Fix PETG Filament That Becomes Brittle
Increase your printing temperature
Dry your PETG filament
Improve your first layer – level bed & use settings
Calibrate your extruder steps
Use a good cooling fan speed
Slow down your printing speed
Increase infill density
Increase wall thickness
Dial in retraction settings
Unclog & clean out your nozzle
For instances when you experience brittle prints with PETG, using one or more of these solutions to try and fix your brittle PETG 3D prints.
I have explained here each of these ways on how to resolve the problem of brittle PETG.
1. Increase Your Printing Temperature
If you find that your PETG is becoming brittle after 3D printing, I’d first try to increase your printing temperature and see if that makes a difference. PETG prints at a relatively higher temperature than most filaments, so you may be experiencing brittle PETG 3D prints due to a low temperature.
Many users have experienced this and figured out that after increasing their printing temperature, they had much stronger and durable PETG models.
The reason why this works is because the higher temperature allows for the filament to melt better, leading to a material which can adhere to the previous layer better.
You want to make sure not to go too high in temperature because it can result in a lot of stringing and oozing.
The usual recommended temperature for PETG filament is anywhere between 240-260°C, along with a bed temperature of 80°C. It’s a good idea to do some of your own testing since there will be slight differences between your environment and another user.
The appropriate temperatures for every filament are usually included in the filament description for every spool. It is good to adhere to the ones stated for your filament as a general rule.
One of the best methods to find the optimal temperature for your filament is to create a temperature tower, which can be done directly in Cura. I’ve used this many times myself, and gotten great results. Check out the video below for the simple instructions.
It’s simply a 3D printed tower which has a number of towers where the temperature changes as it moves up the tower.
If you are printing with PETG, especially on a 3D printer like the Ender 3, make sure to upgrade to Capricorn PTFE Tubing since it has a higher temperature resistance than the stock PTFE that comes on most 3D printers.
2. Dry Your PETG Filament
Another key fix that you want to try out if you find that your PETG is brittle is to actually dry your spool of filament. Many people don’t realize that easily absorbs moisture within the environment after being left out, leading to printing issues and imperfections.
Moist filament can easily be the difference between a weak and brittle PETG 3D print, versus and strong and durable PETG model. It can also give poor bed adhesion which leads to a poor foundation and uneven extrusion.
The moisture in filament can get pretty bad even after just 24 hours if you live in a really humid area, so drying your filament along with proper storage is recommended.
One of the best ways to dry your PETG filament is to get yourself a specialized filament dryer machine like the SUNLU Filament Dryer Box from Amazon. It’s being used by thousands of 3D printer users to dry their filaments with really good results.
You can set the temperature up to 55°C and the timer for up to 24 hours, but 8 hours is usually what works for PETG. One user who did a test on three different filaments (PLA, ABS & PETG) found noticeable improvements, especially in the strength of the 3D prints.
It’s even possible to 3D print while the filament is in the dryer box due to having holes to feed the filament through.
After you dry your filament, they should be ready to 3D print. Get yourself a eSUN Filament Vacuum Storage Kit from Amazon for storing your filaments when not in use.
This particular kit comes with 10 vacuum bags, a 15 humidity indicators, 15 packs of desiccant, a hand pump and two sealing clips.
PETG is a very robust material, but it needs to be taken care of to work effectively.
3. Improve Your First Layer – Level Bed & Use Settings
The first layer is the foundation of your 3D model, so you want to ensure that your first layer is on point. One of the most important facts for a good first layer is to have a leveled build surface. It means that your flow of filament will be even and should adhere better to the print bed.
You’ll either have automatic leveling or manual leveling, so make sure that you level your bed using the usual techniques. The main technique for a manually leveled bed is to use the paper leveling method, or you can try “live-leveling” which is leveling while your nozzle is extruding filament.
If you do adjust the leveling knobs while extruding, you should keep your fingers safe from movements of the bed. One thing I like to do is place a fairly large object in Cura, slice that but with 3-5 skirts.
This allows you to adjust the bed level as the nozzle is extruding around the edges of the print bed until the first layer is laid down nicely.
Check out the video below by CHEP on the standard technique to level your bed.
For automatic leveling, make use of your Z-offset to get a good bed leveling.
Once you have your bed leveled, you can also make use of good first layer settings.
I’d recommend doing the following:
Set your Initial Printing Temperature 5-10°C above your standard temperature
Test increasing your Initial Layer Flow to 105-110%
Try increasing your Initial Layer Height slightly above your standard layer height (from 0.2mm to 0.24mm).
You can also try increasing your Build Plate Temperature Initial Layer by 5-10°C
Keep your Initial Layer Speed between 20-30mm/s
4. Calibrate Your Extruder Steps
Another potential fix that can solve your brittle PETG 3D prints is calibrating your extruder steps or e-steps. This setting is basically an accuracy measure of when you tell your 3D printer to extrude 100mm of filament, it actually extrudes 100mm of filament rather than 95mm or 105mm.
Proper calibration of the extruder for E-steps and proper flow rate of the filament helps can set you up for a strong PETG print.
The steps are fairly simple to get done, and there are many guides that you can follow to calibrate your e-steps.
Check out the video below to get this done.
5. Use A Good Cooling Fan Speed
If your PETG 3D prints are brittle, making use of an optimal cooling fan speed is important. You can use cooling fans with PETG at a low or high speed depending on what you are trying to achieve.
Using a cooling fan on a high speed is great for improving overhangs and overall print quality, but it does cool down layers a lot quicker which makes the layer adhesion worse.
To fix brittle PETG 3D prints, you want to use a lower fan speed of anywhere from 0-40%. You can use the low fan speed and use a good orientation to reduce the level of overhangs on your models so it doesn’t sag or droop.
One user who had issues with brittle PETG prints found that using a cooling fan setting of 30% helped out a lot. Another user said he went from printing PLA to PETG and forgot to turn the cooling off. He experienced bad layer adhesion and cracks simply from removing the model.
After 3D printing the part again without cooling, it came out durable and flexible.
Here is a video comparing fan speeds for PLA and PETG 3D printing.
6. Slow Down Your Printing Speed
Reducing the printing speed can work for fixing brittle PETG 3D prints as well. The default speed in Cura is 50mm/s which should work fairly well in most cases. Some users have mentioned getting better results by slowing down their printing speed even further.
You can try some testing with slower speeds of 20-40mm/s to see how it works, but it will have an impact on your printing times. You can 3D print a few test models with different print speeds and observe the differences.
I’d avoid using print speeds of 70-80mm/s unless you have a really good hotend and a stable 3D printer.
Check out the video below for a useful tutorial on how to 3D print PETG successfully. Slowing down the print speed is one of the key suggestions.
7. Increase Infill Density
Once you’ve done a few of the fixes above, you can try to increase your infill density to make your PETG 3D prints stronger and less brittle. Infill density is great for the internal strength of the model, having a percentage anywhere from 20-60%.
You can also try to increase the Infill Overlap Percentage to improve the connection between your infill and the walls.
Also, changing the infill pattern to Grid or Cubic works for brittle PETG prints and less stringing.
Check this video by Stefan from CNC Kitchen for 3D printing stronger infills.
8. Increase Wall Thickness
As you may have seen in the video above, it mentions shells, also known as walls in your 3D prints to improve strength. To fix brittle PETG filament, increasing your wall thickness can work pretty well since it provides a stronger exterior.
A combination of high infill density and high wall thickness will significantly improve your model’s strength and durability. I’d recommend having a wall thickness of at least 1.2mm, up to 2mm+.
9. Dial In Retraction Settings
PETG is prone to stringing which can cause weaker 3D models. You can fix this by lowering your printing temperature, as well as dialing in your retraction settings. This is an overlooked setting by many users because it’s not one of the basic settings that you’ll hear about.
You usually find out about retraction settings after you have a little more 3D printing experience.
The default retraction settings in Cura typically work fairly well, but it’s a good idea to optimize your settings with something called a Retraction Tower.
It involved installing a plugin directly from Cura and adding a Retract Tower along with the parameters. The process is fairly simple which you can learn in the video below.
A combination of using a slow speed and having good retraction settings can solve a lot of your PETG issues.
Make sure your extruder’s feeder gear isn’t too tight so it doesn’t grind your PETG filament during retractions.
10. Unclog & Clean Out Your Nozzle
Another potential fix for brittle PETG prints is that your nozzle or extruder pathway has some kind of clog or jam. Over time, your 3D printer can start to build up dust and debris, added with the heat which can lead to clogs.
You want to check that your nozzle isn’t clogged up since it results in extruding less material than you are telling your printer to extrude.
A useful technique to clean nozzle clogs is the cold pull method. Check out the video below to learn how to do this. It’s basically putting in a special cleaning filament at a relatively high temperature, letting it cool down, then pulling out the filament manually to clear the clogs.
To check whether your nozzle is partial or fully clogged, try heating up your nozzle to around 200°C and check how the filament is extruding. It should extrude out in a fairly straight line, but if it curls quite a bit, you probably have a clog.
Sometimes, simply using a nozzle cleaning needle can help push out any clogs and jams in your nozzle while heated up.
Replacing the nozzle is also a good idea if you have been printing with it for a long time and have never changed it. The MakerBot Nozzle Set is a good replacement for your 3D printer.
11. Use a PEI Bed Surface
Bed adhesion for PETG 3D prints can be tricky, but you can make things easier by using a good bed surface. One of the best bed surfaces I found that you can get for your 3D printer is the HICTOP Flexible Steel Platform with PEI Surface from Amazon.
It can easily be installed onto your 3D printer by sticking the magnetic side down on your aluminum bed plate, then placing the steel platform with PEI top surface on top of it.
PETG and other materials should adhere nicely throughout your prints, helping to fix any foundation issues that could lead to brittle 3D prints. They even specifically state that PETG works well with this bed, with a bed temperature of around 80-85°C.
Michael Dwamena is the founder of 3D Printerly, a platform dedicated to simplifying 3D printing for hobbyists and professionals alike. Owns over 20 3D printers (filament and resin) and has plenty experience 3D printing. Michael has authored over 900 articles, helping millions navigate the exciting world of 3D printing.
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