Hi all,
I experienced some difficulties with the original BambuLab PETG that I bought together with my X1C and see a lot of topics from people who also struggle to achieve nice prints. At some point, I suspected the filament itself and wanted to know if other brands behave better.
In one of those PETG problem threads another user and me started some tests, comparing BambuLab PETG, Sunlu PETG and IEMAI highspeed PETG, tweaking different parameters like nozzle temperature, print speed, cooling settings, speed reduction at overhangs and layer time. As criteria, I mainly looked at tendency to curl up, loose strands, and surface gloss. As I heard from several sources, PETG that becomes matte is being printed too cold or too fast and suffers from reduced layer adhesion and general strength.
I was surprised by the big differences that I found between BambuLab PETG and the other two, which behaved very similar. But just looking at the gloss didn’t seem adequate to rate the strength of the prints. I quickly came to the point that I wanted to build a pull testing machine, e.g. the one that Stefan from CNC Kitchen published as open source. Thankfully I cancelled that as completely unrealistic and reduced my demand to a simple force measurement.
So instead, I bought a force meter with peak hold function and 500N (~50kg) capacity. I built a little jig and designed a test object. To my surprise, even pieces with 6mm diameter withstood the maximum 500N pulling force easily. Making the diameter even smaller didn’t seem reasonable because it would introduce too much uncertainty. Instead I chose a differnt object, that would create an off axis load, a bit similar to Stefan’s test hook.
The whole project got a bit out of hand. So far I have printed and destroyed more than 150 specimen, testing for different brands and print settings. I thought my results might be interesting for others too, so I want to share them here.
This is the simple jig with the force meter I’m using:
and one of the specimen (please ignore the poor picture quality 
) :
The cross section in the weakest spot is 5x8mm rounded, 4 walls, no infill. The mounting holes are offset by 11mm. This was the result from some iterative steps to optimise print time and material vs. overhang angles and a force that sits nicely in the range of the force meter.
For each combination of brand and settings, I printed 4 specimen to counter sample variation. I added an item that is printed at only 10mm/s to ensure sufficent layer time without using lots of material.
In the beginning, I only printed at 120 and 300 mm/s. Later I appended one test with 30 and 70 mm/s and all later tests were at 70, 120 and 300 mm/s. I did not want to go through all possible combinations but selected them based on prior results. E.g. when I saw almost no difference between 30, 70 and 120 mm/s, I dropped 30 mm/s from the later tests. I also did more extensive tests of fan settings only for the filaments I was most interested in. That is why the population of the table seems quite fragmented. All filaments had been dried before the test and then placed in the AMS.
I also tested some specimen printed flat. I tried to set walls and top/bottom layers so that cross section is as close as possible to the standing specimen, buth there might be differences. So please take those measurements with a grain of salt.
In addition to PETG, I also tested PC and three flavors of PLA.
And for completeness, this is what the current build plate looks like:
Ok, sorry for the very long introduction. This is the table with the condensed results. Only the best results for each brand are shown. The table below has all the information.
And here is the full table with all parameters, individual measurements and including standard deviation as a measure for sample variation:
My takeaway:
- There really seems to be something wrong with the BambuLab PETG. I couldn’t even print the specimen successfully at 300mm/s in more than one attempt, mainly because the overhangs curled up and eventually were catched by the nozzle and kicked the whole piece over. That weak quality already became obvious during the tests for optimal temperature, speed and fan settings. I had zero interest in further investigating it, as the much cheaper contenders were so much easier, more forgiving and stronger.
- The Sunlu is the cheapest and yet comes out on par or ahead of most others. So it is hot contender for my go to PETG.
- The only noticeable step up over Sunlu is german brand dasfilament. Besides highest strength even at 300mm/s compared to others at lower speed, it also printed super nice, no matter which settings I threw at it and strength results were extremely consistent between specimen, where all others had much more variance.
- almost all materials suffer from 300 mm/s while there is almost no difference between 70 and 120 mm/s. It would be nice to have more values e.g. at 180 and 240 mm/s. But I don’t see, starting over all tests. Maybe I will do it later. I will print uncritical pieces at default speeds, but reduce speed to 120 when strength is critical.
- too much cooling really destroys layer adhesion for PETG. That is common knowledge, but it is nice to see it confirmed. Surprisingly, the material profile provided by dasfilament suggests 100% part fan and 70% aux fan, which leads to one of the worst layer adhesion values.
- I totally underestimated, how much load those materials can bear! up to now. I have helplessly overdimensioned most parts that have to carry some load. The cross section of those specimen is really small and they are loaded very unfavorably and still hold up against 15 … 20kg perpendicular to the layers!
- Color seems to have an influence, as can be seen from Sunlu clear vs. white. That too is old news, but it is interesting to experience yourself. I have heard, that especially white often deviates a lot in parameters from other colors. I also have a sealed roll of black Sunlu. I first want to use up all the other open rolls, but eventually will test that too.
- PC really is a different beast, not so much for layer adhesion, but for strength within layers and the way it fails. Where all PETG samples just snapped at critical load, the PC started to yield, then walls separated from top & bottom and only when the walls were fully stretched, it finally gave up. On top there are all those other properties like heat resistance, impact resistance, stiffness, low creep. I will try to also get my hands on the Bambu PC, to see how it compares.
My choice of brands still is very limited, but I really don’t want to buy another bunch of rolls and unfortunately, only few sellers / manufacturers seem to offer samples. If you want me to test different settings with my available filaments or if you send me 50…100grams, I am looking forward to your input.
My next topic for investigation will be creep behaviour of different materials. In my opinion, this is a heavily underrated material property. Yet, there are almost no systematic tests available.
There are two brands that I’m still interested in for PETG. Those are Polymaker and Prusa. Maybe I find somebody among my friends who can spare some.
I’ll be mindful to double check these guys as I use my unopened boxes.