Your thoughts on High Flow PETG

Bambu Lab X1 Series
21

Hi, polymers have a property called the melt flow index (MFI) - it’s how easily it flows under a certain temp. For a given polymer, say PETG, it has to do with the length of the hydrocarbon chains that make up each molecule. Longer chains lead to stronger and tougher parts (because more overlaps between chain pieces) but is more difficult to extrude for the same reason (it doesn’t flow as well, more strings, etc.)

Shorter chains (higher MFI) are generally regarded low quality. As you recycle polymers over and over - heating the chains, stirring them and pushing them around - the chains break and get shorter. In effect, they degrade. However, manufacturers prefer this lower grade polymer because it’s easier to work with - in injection moulding - you can cycle faster, have less voids, etc.

I suspect that this high flow PETG (like the high flow PLA) is just polymer with shorter chains - higher MFI, and thus is mechanically weaker and snaps easy.

The G part already made PET weaker, I think the high flow PETG is a step too much. Generally you would use PETG over PLA for the mechanical properties, so I don’t think there is much need for a HF PETG.

Source: I’m an engineer that designs injection moulded parts (among other things).

Google “melt flow index” to know more.

3 Likes
22

Personally, the HF PETG sounds a bit gimmicky to me. If it’s not performing as PETG should, then I’d go back to the real stuff.

I too am trying to push speed to avoid the VFAs, especially with shiny PETG. The bottle neck is max flowrate. So, to increase your speeds while staying at the same flowrate and temperature (keep stringing reduced), you can lower your layer height. Otherwise you’ll need a high flow nozzle, as mentioned above, to maintain the same speeds, temps, and layer height as you use now.

Or you can bump up temp and try messing with retraction to solve the stringing. I’ve found the default of .8mm a bit short. 1mm seems to work well at most temps for me.

2 Likes
23

its not very good, i purchased 2 rolls and they haven’t updated the firmware in the UK to include this new filament. I can manually add it via the lcd screen on the x1c but then it quickly changes back to “?”. I’ve searched for updates and apparently the firmware is the latest. In both bambu studio and handy PETG HF does not show up.