I put a fresh reel of PLA in my printer and started printed really shiny things. ("Specular highlights" would be how 3D graphic artists would describe it.)

However, a few days later, the prints are coming out a bit matte.

I'm not terribly concerned, although it seems unusual to get such different results from the same reel.

What can possibly cause this?

  • 2
    $\begingroup$ Is your room a bit damp, or humid or steamy? $\endgroup$
    – Greenonline
    Apr 15 at 19:35
  • $\begingroup$ Does it become more or less shiny in humidity? $\endgroup$ Apr 15 at 19:39
  • $\begingroup$ Or have you increased printing speed..? $\endgroup$
    – Greenonline
    Apr 15 at 20:14
  • $\begingroup$ To (potentially) alleviate the symptoms of whatever the issue is maybe try acetone vapor to smooth out the print. Whether that actually restores the desired shinyness depends on the filament but it could work $\endgroup$
    – Hobbamok
    Apr 16 at 8:47
  • 1
    $\begingroup$ @Hobbamok - good point. There is a question about that somewhere, from long long ago, I'll try to find it. Here you go: How do I give 3D-printed parts in PLA a shiny smooth finish? $\endgroup$
    – Greenonline
    Apr 16 at 8:48

1 Answer 1


In short, PLA filament is somewhat hydrophilic.

When you first unwrapped your reel of filament, it can be safely assumed that it came from the supplier nice and dry (unless you have a dodgy supplier). Hence your nice shiny prints.

After a few days, once unwrapped, that filament will have slowly absorbed humidity from the air in your room, unless you have a carefully controlled environment.

As the filament absorbs the water in the air, when going through the hot nozzle, that water will expand at a different rate to the filament, creating various gaps and inconsistencies in the resulting print. These inconsistencies will make the final print surface appear less shiny, or matte.

At the extreme, after an extended period of absorbing water, very damp filament will start to pop and crackle at the nozzle (as the water turns to steam) and create brittle prints with a very bad finish, with pits and bubbles and look very ugly.

I suggest sorting out the environment of the room, and at the very least get a dehumidifier or store the spool in a box filled with silica gel. There are other measures that can be taken, but that is beyond the scope of your question, which was about the matt finish.

See also Filament storage?

  • $\begingroup$ Does the matte surface affect the strength or is it just cosmetic? $\endgroup$ Apr 16 at 11:00
  • 3
    $\begingroup$ To quote the above: ... and create brittle prints... $\endgroup$
    – Greenonline
    Apr 16 at 11:02
  • $\begingroup$ It will start cosmetic, but as the plastic absorbs more water, part quality and strength will also degrade. $\endgroup$
    – user10489
    Apr 28 at 12:40

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