The do-it-all 3D printing filament: PETG! Learn what the differences are between Copolyester and PET and how to best print the materials.
PETG or, more widely speaking, the range of copolyesters! It’s like PLA and ABS had a lovechild with all the best bits from either one. Copolyesters have a good mix of properties and has become my personal favorite, but there are some things it can’t do or will need extra tuning for. Let’s go through those!
What is PETG?
There is a bit of confusion around what you should call these materials -- is it PET, PETG, Copolyester or CPE? Well, pretty much only Ultimaker calls them CPE, which is just a fancy abbreviation for CoPolyEster. Many manufacturers have their own brand names for various types of copolyesters, be it Colorfabb XT, HT or NGEN, Taulman T-Glase or simply PETG.
PET itself, or Polyethylene terephthalate, is actually not what you’ll typically 3D print, that would be PETG or the glycol-modified version of PET. The glycol content keeps the plastic from crystallizing, making it a bit softer, chewier and having it melt at a lower temperature -- pretty much ideal for 3D printing on the common machines. PETG print at around 230°C, pure PET at 260°C or more.
Aside from that fundamental difference, filament producers can also modify the plastic to have different properties for how they perform while being printed or in the finished printed part. No two PETG materials are going to be exactly the same, but typically, they’re pretty close when it comes to how they need to be printed or how the parts will behave.
Ok, so how do these need to be printed? Well, for a base tune, grab a PLA profile you know works for you -- or simply your slicer’s default profile -- then reduce the part cooling fan speed a bit, 20 to 50% work well on most of my printers and adjust the temperature to match what your filament manufacturer suggests. If there’s no recommended temperature, try 230°C and increase it if you see bad layer adhesion or extruder jams or decrease if you see excessive stringing or curling or other overheating artifacts.
On the topic of stringing, most PETGs will want to string quite a bit because even the molten PETG still doesn’t easily tear, but will keep pulling that fine string out of the nozzle. It’s a good idea to increase the retract length by a bit even before your first print, maybe add a millimeter for a direct extruder and two or three for a bowden. If you still get strings, you either have the option of just burning them off with a hot air gun or tuning your printer’s retraction even further. But you can’t just increase retraction length like crazy because you’ll end up with blobs instead. What you should into is the retraction speed settings -- try a slightly faster or slower one and it might just be that last piece of the puzzle to help you get a clean print. What’s always going to help with both stringing and blobbing is increasing the travel speed between retracts. Travel moves should always be as fast as your printer can handle, because it’s going to give the hotend as little of a chance of oozing and going out of the intended plastic flow situation as possible if that makes sense. Your printer’s firmware should know how fast it can reliably go, so you can actually set the travel speed on your slicer to some obscene value and let your printer handle the rest.
One more note about printing copolyesters: Whatever you do, don’t print them directly onto glass. Even though it’s kinda hard to stick copolyester parts together when you actually want them to stick, they will actually fuse to some glass print surfaces and take chunks out when you try to remove them. PEI and other films are a similar story, so I’d always recommend using some extra layer of adhesive on top.
With those base settings, PETGs and other similar copolyester materials should easily make for clean, strong and attractive prints. So what do you use it for? Well, anything, really.
PETGs can do most things a PLA would be able to do when it comes to printing detailed parts or larger ones without warping too much. It also has many of the upsides of ABS like being reasonably temperature resistant up to around 70° or 80°C, which is a bit lower than ABS; but still good enough for many parts that you’d use with motors or electronics. Prusa even uses them for everything on the MK3 now. PETGs are also really strong and came out with consistently impressive results in the filaween tests, but their strength, even though it is good, I feel is a bit less predictable than other materials because some copolyester prints like to shatter instead of gradually failing. What can make this behavior much worse is when you use “wet” PETG -- through a process called “hydrolysis”, the water steaming up as the plastic gets heated will essentially tear apart the polymer chains and make the plastic more brittle -- so keep it dry and if you feel like your spool of filament has been degraded, chuck it in the oven at 60°C for an hour or two.
Copolyesters also comes with the huge benefit of being really clear and transparent if, of course, you get the transparent versions. With the right settings, you can get some amazing looking parts out of it!
Mating PETG parts
Just like ABS, you can use metalworking tools with PETG prints no problem, but painting or gluing parts can be a bit tricky. If you ever tried to glue or paint a plastic water bottle, you’ll know that nothing sticks to this stuff. If you need to connect two Copolyester parts, there are some options for solvent-welding, but they are some pretty nasty substances involved. What the company 3M recommends is a few things: With any adhesive, you can prepare the surface either by roughing it up with some sandpaper and then cleaning and degreasing it well or by actually activating the surface with a bath in 80°C caustic soda for a few minutes -- but please be really careful when trying that and follow the usual safety rules. After that, they recommend regular superglue, polyurethane-based resins or -- tape! If you’ve ever stuck a GoPro to anything, you’ll know how well that VXB tape sticks to stuff, so the chances are good that it’ll actually stick well enough even to PETG parts straight from your printer.
But in the same spirit, PETG is a much more “friendly” plastic than some others. It doesn’t smell when printing and many filaments are actually food-safe if printed right, it’s resistant against many chemicals including, surprise, glycol, the hard-tubing for PC watercooling, where glycol is a common water additive, is actually often made from PETG these days. Also, PETG and copolyesters themselves are UV and weather resistant, so the parts are going to stay strong and usable outside, but the color might fade after a while in the sun.
Overall, it’s just nice to print and for most use cases is still close enough to PLA where it’s no big hassle to print, but still gives you parts that are actually stronger than ABS and come with almost the same temperature resistance. And your good, base-level PETG isn’t even much more expensive than PLA, but of course, you can get it in all sorts of specialized properties and price ranges if you’re into that.
Let me know what your experiences with this relatively new material are! I know I like it a ton and it has basically replaced ABS for me. On the topic of ABS, a few of you have commented on the last video that I completely left out vapor smoothing for ABS. So, I actually rarely vapor-smooth a print because it’s a bit too much of a hassle, but I’d be really interested to hear from you all if that’s something you do to your prints. Regularly. Or if it’s just a “eh, maybe twice a year” kinda thing.
Thank you to Aprintapro for sponsoring the series! Check out their filaments here
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