Oct. 21, 2016
PETG is an abbreviation for Polyethylene Terephthalate (with a glycol modification) which is one of the most common polymers used today. It’s used to make water bottles, food packaging, and countless other common plastic items. As a 3D printing filament, PETG plastic has proven its worth as a durable material that is easy to use. Figuratively speaking, it combines the most useful characteristics of ABS filament (the rigidity and mechanical properties for functional parts) with the ease of printing that PLA filament affords. Kind of a “best of both worlds” scenario.
You’ll often see references to PETG in one or more of the following forms: PET, PETE, PETP, PET-P, PETG, GPET, PETT, and others. These can be confusing to someone who is trying to understand the differences between them and what effect any of the suffixes would have (if any) on their 3D printing experience.
PETG is the most common form of PET used for 3D printing filament. The G stands for glycol-modified, and this makes the resulting resin more clear and less brittle than raw PET. Raw PET typically isn’t used for 3D printing. PETE, PETP, PETT, and PET-P are modified versions of PET (called copolyesters), but by far the most common material used in 3D printing is PETG.
For the purpose of this article, I’ll use PETG as a catch-all term to describe the different variations of the 3D-printable filament.
Designed by FMMT666 and printed in PETG
Quality PETG filament, like MatterHackers' PRO Series, is a necessity if you want a good PETG print. Poor-quality PETG or PETG that isn’t sufficiently dry will not print properly which can cause issues and waste time.
PETG is hygroscopic, which means it will actively absorb moisture from the air. For this reason, PETG plastic should be stored in a cool, dry place, and dried if exposed to humid air for too long. What constitutes “too long” depends on the relative humidity in the air, but when it comes to 3D printer filament, it’s best to err on the side of making the filament “too dry” rather than allowing it to be a “little wet.”
Printing wet PETG can lead to hydrolysis which will permanently alter the filament on a molecular level, making it significantly weaker than it would be if it were printed dry.
Check out our in-depth article on how moisture affects your filament, and how you can successfully dry your 3D filament here.
Vacuum-sealed bags and desiccant packs ensures that the filament is exposed to as little moisture as possible. Sometimes a bag can get punctured and lose the vacuum seal, but so long as the whole thing is packaged with a desiccant pack that should be sufficient to absorb enough of the moisture for the filament to print properly-- at least until unpacking.
Vacuum sealed PRO Series PETG
All printers are not created equally. Some have features that others do not, and there are some specific requirements to print PETG.
To print PETG, your printer must be equipped with a hot end that can reach a temperature of at least 235°C. Ideally, you’ll want to be able to reach about 265°C, but 235°C may be sufficient for some PETG filament. Keep in mind that every spool is unique, and may require a slightly higher or lower temperature.
An all-metal hot end like the E3D v6 works great with PETG.
E3D v6 All-metal Hotend
PETG will typically flow nicely in the range of 230-265°C. Print too hot and excessive stringing or blobbing will occur; too cold and it may jam or delaminate easily. Since exact thermal properties vary from spool to spool, you’ll want to experiment with any filament you buy to determine the best temperature at which to print.
As it is with printing any type of filament, getting a good first layer is essential to a successful print. Without a good first layer you will likely need to reprint the item, so it’s imperative that you know what it takes to start a print off right so it can build to completion.
I experimented with a few different types of beds and adhesion methods, and the best practices I found are listed below.
Printing on Blue Painter's Tape
Blue painter’s tape, with or without heat, is the best surface for printing PETG plastic. The finish on the bottom is fairly smooth, but not glass-like.
The top of the cube shows the smooth finish when printing on blue painters tape
Printing on glass
Glass is very smooth, which imparts a glossy surface onto the printed part. Printing on glass requires a heated bed. We find that unscented hairspray on a heated bed (50-60°C) works best on bare glass.
Other Print Bed Surfaces
BuildTak printing surface works well with PETG filament. It’s a universal bed surface, so it will also work with PLA and ABS without the need for switching plates or surfaces. It will wear down over time, but prints stick very well.
Keep an eye on how much filament doesn’t end up where it’s supposed to. PETG plastic is prone to stringing and oozing, so watch for filament that ends up stuck on the nozzle. Sometimes blobs of PETG filament will stick to the nozzle and then end up deposited on another part of the print where it’s not supposed to be. If this happens it will cool and harden, which can be a hazard for the nozzle the next time it moves into that space. The result is usually a layer shift, which can be detrimental to the print.
When changing filament from something else to PETG, you’ll want to heat the hot end to at least the temperature required to melt the other filament, though PETG’s print temperature would be ideal unless the other material melts at a higher temperature than PETG.
Once the PETG filament is flowing nicely and all remaining traces of the previous filament no longer come out of the nozzle in chunks or flow, you’ll be ready to print PETG.
When changing from PETG filament to another filament, heat the hot end to at least PETG’s melting temperature or a little hotter. Once you feed the new filament in you can adjust the hot end temperature to match that filament’s melting temperature.
One of the hidden powers of PETG plastic is that the flex of the material lends itself to being used for snap fits. When designed correctly PETG can have a very strong snap fit for functional closures or latches.
PETG has a shrink ratio (or shrink rate) of less than 0.004 in/in so printing large surfaces are not a problem when printing on a well-leveled surface.
Use of supports can easily be accomplished when using PETG plastic but a larger air gap maybe required for easy removal from the main body.
Several issues can arise during a PETG plastic print. Here is an overview of some of the more frequent problems with printing PETG filament and steps you can take to correct them:
If PETG filament globs onto the nozzle and gets dragged around instead of sticking to the bed:
Make sure you have the right bed surface for PETG: 1) blue painter’s tape without heat with or without gluestick, or 2) plain glass needs heat and (unscented) hairspray.
Make sure you’re printing at the right temperature and that your bed is the right temperature. 230-265°C extrusion temperature. 50-60°C bed temperature
Make sure the print bed is level. Use Software Print Leveling to be sure.
Make sure the extruder is at the right height, and if not either 1) adjust the Z Offset for the extruder or 2) adjust the printer’s limit switch (if equipped).
Check the ambient temperature. If it’s too cold, your print can be negatively affected. Ideally you want it room temperature or hotter for PETG.
When filament intended for the infill and/or top surfaces ends up globbing onto the nozzle instead:
Make sure the extrusion temperature is not too cold. If you’re closer to the lower end of PETG’s printable range (230-265°C), bump up the temperature five degrees at a time until extruded filament flows nicely out of the nozzle and stays where it’s extruded.
Slow the print speeds down 10-20%, either with or without bumping the temperature up. Speed and temperature are directly related with regard to getting a nice flow.
Check the filament tension.
Clean the filament drive gear (if needed).
Artifacts on the outside of printed parts can occur for various reasons.
If your printer stutters when connected to a computer:
Make sure that the computer is not too busy to feed the printer commands. Running applications other than the printer-control software at the same time as a print will use a part of the computer’s memory. If enough memory is used by other programs it is unavailable for the printer communication and the print may suffer.
Print from SD card. On some printers you can try and print from SD card. This often helps the printer have enough data to run more smoothly.
If the filament pops as it comes out of the nozzle:
Dry the filament. Wet filament will hydrolyze as it melts and will be significantly weaker than filament printed dry.
Source better filament. The quality of your filament will have a big impact on the quality of your part. Getting better quality PETG filament will help you produce better parts. However, don't be too quick to assume the problem is in your PETG. With good settings and patience, hobbyists have succeeded in printing all sorts of materials many of which have very low viscosity and inconsistency. You should be able to get at least usable parts even with some lower quality filament and the right settings.
Turn on cooling fans for that section of the print.
Lower the temperature and speed.
Print more than one part to give the layers time to cool as the nozzle works its way back and forth between the parts.
Use a small fan. If your printer does not have an integrated fan you can use a small desk fan. Just make sure that the fan does not cool the hot end.
While it does not happen with PETG as much as with some other filaments (like ABS filament), warping can occur and destroy an otherwise perfect print.
If this happens, use more bed adhesion (depending on your bed surface). 2-3 layers of gluestick on the bed is usually enough for sufficient first-layer adhesion on blue painter’s tape, and a 2-3 second spray of hairspray should suffice for glass prints.
Avoid uneven gluestick application, or incredibly thick layers of it that could interfere with the print.
If the extruder is turning properly but no filament flows:
Make sure your hot end is getting hot. Check that the hot end is heating at all. If it is not you need to have your printer serviced or figure out why. It is likely a loose connection or that the electronics board suffered a short circuit (assuming the printer is still connected and responding to your host software).
Slow down the print speed. If your hot end is hot but the print is going too fast, the filament might not be able to fully melt before it’s pushed through the nozzle. If this happens, back pressure can build up and the filament will start to grind against the extruder gear.
Clean the drive gear and adjust tension. If the extruder gear grinds on filament, over time the gear will have less grip. You’ll need to clean the gear with a brush to get the tiny pieces of plastic, then make sure your tensioner is solid against the filament. Too much tension can also prevent extrusion and is more common with direct drives.
Remove the any obstructions.It may be that you have a small particle in your extruder tip jamming the plastic. Push some filament through by hand to clear any obstructions and allow the filament to flow nicely.
Check for and remove jams between the extruder and hot end.While uncommon with PETG, jams can still occur. If the filament breaks off in the hot end or a piece won’t come out you might have to take your hot end apart, clean out any pieces that aren’t where they’re supposed to be, and put everything back together again.
Thank you for reading How To Succeed When Printing In PETG.
If you have any comments or contributions, please drop us an email or give us a call. We are always looking for tips, and best practices - and would love to hear from you. Feel free to reach out with any specific questions on the MatterHackers Forum.
Happy Printing! - MatterHackers
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