What the f**k was in my filament?!?!

Bambu Filament and Accesories Filament
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So I was having trouble with some BL PLA Marble feeding through my AMS hub, assumed it was the hub as this was where it was getting stuck. Took that apart, no obvious jams/debris, back to the drawing board. Anyway after a few feeding attempts, the filament eventually snapped. Pulled it out and found some sort of melted bug (for want of a better description) embedded into the centre of the filament. BL (or Sunlu or whoever makes this particular filament) need some pest controllers in their Quality Control Team it seems :rofl:.

PXL_20260307_222735907.MACRO_FOCUS
PXL_20260307_222735907.MACRO_FOCUS1920Ă—2560 65.1 KB

PXL_20260307_222751200.MACRO_FOCUS
PXL_20260307_222751200.MACRO_FOCUS1920Ă—2560 70.3 KB

PXL_20260307_222743475.MACRO_FOCUS
PXL_20260307_222743475.MACRO_FOCUS1920Ă—2560 67.1 KB

2 Likes
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Ah yes, the melted bug. You see bambu lab adds this for texture… :sweat_smile:

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GitHub is the best place to submit bug reports.

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It’s a natural coloring agent, none of those nasty artificial chemicals. Just like Cochineal (Dactylopius coccus insects) is used as a coloring in some foods.

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Yes, I was going to ask OP to submit a literal bug report :slight_smile:

I copied and pasted OP’s post into ChatGPT and asked how likely it is for a bug to be embeded into the center of the filament during the filament extrusion process. Here’s what it says (don’t get mad at it - it can only analyze based on the data it was trained on.

[Begin of ChatGPT output]

Short answer: A bug being embedded during filament extrusion is extremely unlikely. What you’re seeing is far more likely to have entered the filament path later (AMS, PTFE tube, extruder, or nozzle) and then became partially melted and pushed into the filament.

Let’s break down the possibilities.

:one: Bug inside the filament during manufacturing (very unlikely)

During filament production:

  • PLA pellets are melted around 180–220 °C

  • The melt is filtered through a metal screen pack

  • The filament is pushed through a small extrusion die

  • Then it is water cooled and spooled

For a bug to end up inside the filament, it would have to:

  1. Survive inside the pellet feed system

  2. Pass through the melt filter screens (which trap debris far smaller than a bug)

  3. Go through the extrusion die (~1.75 mm opening)

  4. Stay intact while surrounded by molten plastic

That combination is basically impossible in a modern filament line.

If something organic got in upstream, the screen pack would catch it immediately.

:two: Something entered the filament path later (much more likely)

Looking at your photo, the dark spot appears at the center of the filament cross-section after it snapped. That can happen if something:

  • Gets sucked into the nozzle

  • Gets picked up by molten plastic

  • Then gets pushed backward or smeared into the filament core

Possible entry points:

:ant: Inside the nozzle or hotend

A small insect could crawl into a cool nozzle when the printer is idle.

When the nozzle heats:

  • The bug carbonizes

  • Molten PLA mixes with it

  • A small chunk can get pushed into the filament during a retraction or clog event

This would match the black charred center look.

:thread: Inside the AMS / PTFE path

Less likely but possible:

  • A small insect or debris gets into the AMS hub or PTFE tube

  • The filament pushes it forward

  • It reaches the hotend and gets partially melted

However, in this case you’d usually see the debris on the outside of the filament, not embedded in the center.

:fire: Carbonized filament contamination

This is actually the most common explanation.

Old PLA inside the nozzle can:

  • Overheat

  • Carbonize

  • Break loose

When that carbonized chunk gets pushed into new filament it can create a black “inclusion” that looks organic.

People often describe it exactly like this:

“Looks like a bug, but it’s actually burnt plastic.”

:three: The clue in the photo

What I notice:

  • The filament snapped cleanly.

  • The dark spot is very small.

  • It looks charred and glossy, not structured like an insect.

Real insects usually leave:

  • visible legs

  • wing fragments

  • irregular shapes

This looks more like a tiny carbonized plug.

:four: Why it caused a feeding problem

A hard contaminant in the filament core can:

  • Increase stiffness

  • Jam slightly in AMS hub rollers

  • Cause filament snapping under feed pressure

That matches the behavior described.

:white_check_mark: Most likely explanation

Carbonized PLA from the hotend or a small contamination particle that got pulled into the melt zone.

:cross_mark: Least likely explanation

A bug embedded during filament manufacturing.

A quick test you can suggest

If they still have the spool:

  1. Cut several sections of filament

  2. Look at the cross-sections

If it were a manufacturing defect, you’d see more inclusions along the filament length.

If it’s clean everywhere else, the contaminant entered in the printer, not the spool.

If you’d like, I can also show you three real failure modes that create “bug-looking” blobs in filament, and one of them is shockingly common with Bambu printers. :toolbox:

[End of ChatGPT output]

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The carbon is probably from the extrusion process. We have that happen at work and usally when it starts they have to pull the die and clean it. Not sure why bambu didn’t just say sorry it happens some times.