PETG generates blob - How do I print this? (Printing help)

RE: PETG generates blob

Harald Kylin — Wed, 15 Apr 2026 06:12:44 +0000

PETG blob problems started for me when I switched from Cura to Prusa Slicer. With the same spool and the filament directly coming from the dryer the blobs came out like pimples on a teenager.

The problem finally settled down after a while. I finally settled on a “detraction extra length” at -0.05, but it was verry weird.

RE: PETG generates blob

mnentwig — Sat, 11 Apr 2026 08:03:55 +0000

Posted by: @kentm
I thought about that, I have the filament in a dry box where the humidity is currently 15.1%. I change the desiccant at 18-20% but I will probably go ahead and do that now as I am waiting on a new nozzle. Otherwise I am going to search the website for that procedure.

That's a common misconception - a dry environment does not automatically dry humid filament. It just stops it from getting humid.

Drying needs elevated temperature to drive the moisture out, for several reasons (diffusion speed, "knocking the water molecules loose" from the polymer). You'll need to actively dry the filament, and probably things will look different after that.

RE: PETG generates blob

KentM — Fri, 10 Apr 2026 20:22:51 +0000

I thought about that, I have the filament in a dry box where the humidity is currently 15.1%. I change the desiccant at 18-20% but I will probably go ahead and do that now as I am waiting on a new nozzle. Otherwise I am going to search the website for that procedure.

RE: PETG generates blob

mnentwig — Fri, 10 Apr 2026 19:48:37 +0000

note, PETG does absorb moisture, quite badly actually if quality matters (to an extent that you may see degradation over the duration of a large print, unless the spool is kept in a drybox). So "humidity" is the first factor to rule out, otherwise everything else is futile.

RE: PETG generates blob

KentM — Fri, 10 Apr 2026 19:31:22 +0000

It's funny that I have also fallen victim of these blobs using PETG. For over a year, I was convinced that PETG was the magic bullet for my 4 year old MK3S+. But I found a post just a few days old with similar issues. Can someone point me to a guide for doing this Linear Advance calibration. For so long now, my machine just worked. I design a part, do a first layer cal and then print it. Am I overlooking some regular procedure, other than routine maintenance, that I should be doing?

RE: PETG generates blob

Harald Kylin — Wed, 08 Apr 2026 08:44:18 +0000

I found another setting that helps. "Detraction extra length" is an amount of material that is punched out through the nozzle after every retraction. On my printer it was quite severe. I had to set this number to 1 to get rid of my problem.

RE: PETG generates blob

geekhunter — Wed, 08 Nov 2023 02:09:35 +0000

Thank you! 0.97 did the trick! I was fighting with crazy blobs and stringing and kind of at a loss. Ran into this thread and this setting solved everything. Thanks!

RE: PETG generates blob

pcweber — Mon, 25 Jan 2021 16:50:11 +0000

I have to agree with bobstro, I have been battling this, and didn't want to adjust the flow from my calibrated extrusion multiplier. I need my parts to fit together tightly. So I have reduced this plus blobs and zits by doing the Linear Advance calibration dialing in each filament that has no profile on this site adjusting the K-Factor as in the calibration routine has made this problem become history. Good luck.

RE: PETG generates blob

bobstro — Sat, 18 Jan 2020 21:04:59 +0000

Posted by: @h-waibel
So my probably overly simplistic understanding is that the extrusion multiplier is a general modifier that is applied to all individual parameters that deal with extrusion (bridge speed, if speed, etc...)?

My understandings is that it's used for calculating any gcode involving extrusion, yes.

RE: PETG generates blob

hawai — Sat, 18 Jan 2020 20:23:36 +0000

Thank you very much bobstro, I slowly start to get a vague idea...

So my probably overly simplistic understanding is that the extrusion multiplier is a general modifier that is applied to all individual parameters that deal with extrusion (bridge speed, if speed, etc...)?

At least it now makes sense to me why it is in the filament specific parts of the settings.