How To Fix Pro PCTG Filament Buildup On Your Nozzle

Infill Setting

The first thing to change is to make sure that you're not using Grid infill.

Grid infill tends to be one of the worst patterns for nozzle contamination and material buildup because of how the toolpath forces the nozzle to interact with already-laid filament.

Grid infill creates self-intersections in the same layer

Grid is essentially two sets of straight lines at 90°.
Unlike gyroid or lines infill, the nozzle physically drives across previously extruded strands within the same layer.

What happens physically:

• First pass lays molten filament.

• Second pass crosses over it while it’s still warm.

• The nozzle scrapes and reheats the first strand.

That scraping action causes:

✅ softened polymer to smear onto the nozzle
✅ tiny strings to wrap around the nozzle tip
✅ additive/filler particles (CF, mineral, pigment) to accumulate

For materials like your Pro PCTG or PET-based copolyesters, which stay rubbery longer than PLA, this effect is amplified.

Vertical pressure points = “micro plowing”

When the nozzle crosses an intersection:

• Z height is constant

• But the filament bead underneath is not perfectly flat

So the nozzle experiences localized upward force.

This causes:

• slight extrusion backpressure changes

• micro under-extrusion after crossings

• molten filament pushed up around the nozzle shoulder

That molten collar is the start of nozzle boogers.

This is why you’ll often see:

clean print → suddenly a blob forms mid-print → drags across surface

Grid infill is basically a repeated blob generator.

Heat + dwell time increases stickiness

Grid infill also has more:

• sharp direction changes

• deceleration points

• dwell time at intersections

Those pauses let material:

• stay hot longer

• oxidize slightly

• adhere to brass or hardened steel tips

PETG/PCTG especially likes to stick during slowdowns — something you’ve likely seen on the X1C with certain profiles.

Why gyroid, cubic, or lines behave better

Patterns that reduce buildup share one trait:

👉 No direct same-layer crossings

Examples:

• Gyroid – continuous flowing motion, minimal scraping

• Lines – parallel passes only

• Cubic – intersections happen across layers, not within one layer

Result:

• Less nozzle contact with warm plastic

• Lower contamination rate

• More stable extrusion pressure

Speed and Acceleration Settings

One of the biggest settings you should change that will cut down that buildup you're experiencing is to drop your acceleration rates in your Process settings under the Speed tab. (in Bambu Studio or Orcaslicer, for reference)

Bambu Studio defaults to 10,000 mm/s^2. I recommend dropping that to 500 or 1000 mm/s^2.

The reason this makes a difference is due to the fact that the toolhead does not have balanced mass above and below the gantry and when it makes a dramatic direction change with fast acceleration rates, it causes the toolhead to tip ever so slightly. 

Because Pro PCTG is a viscous material, it stays where you place it. This means that the previous layer of the print can have a "crown" to the extruded material and the tipping of the toolhead causes the very top of that crown to be scraped and then build up on the nozzle.

We really need to address this via a Process profile for Pro PCTG, as this setting is not a part of our Pro PCTG Filament profile.

I hope that this feedback helps you to be more successful in printing Pro PCTG.