I've noticed this on almost ever print I've ever had. On the initial first line that clears the extruder nozzle tiny little bubbles/craters seem to form on the line. While I don't think these are causing any issue with my prints I'm curious to know the reason why they form at all.

Is this due to water absorption in my filament that turns to steam, which then bursts through the molten plastic? Is it due to air bubbles in the filament that are cause by the manufacturing process of the filament? Or is this more an indication that my nozzle is damaged or clogged in some way?

Bubbles in extrusion

This image was made using ABS plastic and a heated build plate. I've noticed these same 'bubbles' appearing using PLA, and Nylon.

Edit: Nozzle temperature 240°C, build plate temperature 150°C, Nozzle diameter 0.4 mm, filament diameter (measured 1.75 mm) retraction distance 1.7 mm. Using the Makerbot Desktop Slicer.

The first line that my printer extrudes, where I'm seeing these 'bubbles' is a nearly full line. Makerbot starts from the right side of the image, extruding to the left.

Single line extrusion on printer bed

  • $\begingroup$ Please provide the head temperatures, feed rates, nozzle diam, etc. What I see in the picture looks more like a startup problem of the nozzle feed "chamber" not being completely filled yet. Try preheating the head and manually forcing the filament in so that a couple inches are extruded before initiating the print code. $\endgroup$ Commented Jan 19, 2017 at 14:45
  • $\begingroup$ The last 10 prints i've done seem to be looking like the 'bubbles' occur more often right at the beginning of the print/ first line. Would this be more indicative of a retraction setting issue do you think? $\endgroup$
    – Diesel
    Commented Jan 20, 2017 at 17:02

6 Answers 6


Oh yeah, that's simple. You are printing too hot and are literally boiling the plastic. Else you have water. However if it was water you would hear Crackling as it printed. If it is too hot you will not hear nearly as much. I am 87.341% sure you are printing too hot.

Looking at your printing temps you are without a doubt printing too hot.

From this link on 3d hubs.

PLA (Only on Replicator 2) Print temp: 210°C (at 100m/s) Notes: heated bed optional between 40 and 60°C

ABS (Only on Replicator 2X) Print temp: 230°C (at 100m/s) Notes: heated bed at 110°C

  • 1
    $\begingroup$ I'll give it a try at lower temps, (was at 240C for ABS). I've been raising the temp to try and improve the top layer/last layer thinking that I was running a bit cold. Might have to open another question on that instead now :) $\endgroup$
    – Diesel
    Commented Jan 24, 2017 at 17:25
  • $\begingroup$ In those cases you want to lower your solid infill speed. That way it goes slower on those layers and adheres better. Speed and Temp are always in opposition. $\endgroup$
    – StarWind0
    Commented Jan 24, 2017 at 17:54
  • $\begingroup$ Very useful information. This is what was causing my bubbles so if the feedrateis too slow it will get too hot and be boiling. $\endgroup$ Commented Oct 30, 2017 at 22:37

In my experience, bubbles like this are caused by the filament absorbing moisture, which then cooks out at the high printing temperatures.

See: http://reprap.org/wiki/Print_Troubleshooting_Pictorial_Guide#Material_Handling.2C_Material_Contamination_01

  • $\begingroup$ Would you expect a new roll of filament to have water absorption? Or would you recommend cooking/drying out a new roll? $\endgroup$
    – Diesel
    Commented Jan 20, 2017 at 16:58
  • $\begingroup$ If the roll didn't arrive in an airtight bag, with desiccant, I would expect water to have been absorbed, yes. $\endgroup$
    – Davo
    Commented Jan 20, 2017 at 20:29
  • $\begingroup$ Probably not water then, It's a new roll, air tight sealed with a desiccant in the bag. $\endgroup$
    – Diesel
    Commented Jan 23, 2017 at 15:19

I had a similar issue with my Prusa i3 mk2. In researching what could cause extrusion to be nonuniform, I found that it could be due to a number of things:

  • Nozzle height
  • Flow rate
  • Bed/Nozzle/Ambient Temperature
  • Improper bed leveling
  • Dirty reservoir or filament
  • Low quality filament
  • Hardware failure
  • etc...

For me, the problem happened to be a hardware failure where the screw that held the pulley in place on the extruder motor had stripped somehow and the pulley was slipping as the printer was trying to extrude. I temporarily fixed this by using a slightly bigger screw, but was able to get a new pulley/screw piece from Prusa Research to replace the part.

  • $\begingroup$ was retraction rate/distance one of the variables that fell under the etc. heading? I'm noticing that the bubbles occur predominantly at the beginning of the first extrusion line. $\endgroup$
    – Diesel
    Commented Jan 20, 2017 at 17:37

I have spent many hours testing my Anet A8 to resolve the popping issue. The symptoms are similar to yours, Diesel. Both ABS and PLA, different manufactures, good packaging, as well as various sizes of nozzle, are producing bubbles.

I was experimenting mainly with two variables: nozzle temperature and retraction length. Other related parameters I kept fixed:

  • Material: ABS
  • Nozzle size: 0.5 mm
  • Retraction speed: 45 mm/s
  • Travel speed: 50 mm/s
  • Print speed: 40 mm/s

Retraction length

Originally it was set to 4.5 mm. I found it to be impacting the amount of popping significantly, especially in the range of 0.5 mm to 2.5 mm. The optimal value appeared to be in my case 0.8 mm. A lower value would produce even better results in terms of surface quality, but would also start producing oozing.

One important side note is that at the retraction length of 4.5 mm, leaking of the material during idle moves was significant and was becoming even a bigger contributor into gaps in the print strikes (immediately following the idle moves), than popping. This observation is kind of contradictory, but I am making no mistake here. Too large of a retraction apparently may have the inverse effect on leaking/oozing.

Nozzle temperature

Originally was set to 250°C. 260°C produced significantly worse results. 240°C is where I stopped.

Based on some other research, including talking to my friend who successfully uses the same plastic at 260°C, I made the conclusion that the quality of my print head assembly is not perfect, and that it is the main cause of the problem. By finding the perfect retraction/temperature combination I simply mitigated the air sucking in the head, which could be not happening at all if I had used a better quality extruder and nozzle in the first place.


The temperature is too high or your keep your filament in open for days. So that filament observe water from air do the following steps:

  1. pla 190-220 abs 220-240

  2. If temperature in range then bake your filament at 50-60 temp.


There is only one way to find out, which is by isolating any reasons, starting from the simplest one:

  • Firstly, clean and check, or change, your nozzle;
  • Secondly, if that does not work, then change the filament, or find a way to get it dry (some people, with some filaments, use an oven to get moisture out - careful, don't burn it);
  • Finally, change filament brand and get a better quality filament or another type of filament.

Another reason that it does not extrude consistently, is that what you mention as [appearing to be] bubbles maybe [intentional] gaps [in the print].

  • 4
    $\begingroup$ He said he's used 3 different materials. I strongly doubt all of them had mosture problems. $\endgroup$ Commented Jan 19, 2017 at 19:23

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