TL;DR: The flushing volume is how much filament the printer purges on every color swap. Set it too low and the old color bleeds across the boundary; too high and you waste filament and time. Print the flush calibration model with volumes at zero, read the printed value where each transition finally goes clean, add a small buffer, and type those per-pair numbers into the Flushing volumes table in OrcaSlicer or Bambu Studio. Below: why painted 3MFs feel this more than most prints, the five-step calibration, and how to read the result.
Why does a painted 3MF need its own flushing-volume pass?
A painted 3MF assigns a color to every triangle, so a figure with eyes, trim, and a base can trigger dozens of filament swaps over its height. Every swap purges the old color out of the nozzle before the new one prints. If the purge volume is too small, the previous filament hasn't fully cleared and it streaks into the first millimetres of the new region. That reads as bleed at a boundary you painted sharp. Calibrating the volume once fixes it across the whole print, and usually trims waste at the same time.
This is the print-time half of clean boundaries. The mesh-side half, keeping the painted edge crisp before the slicer ever sees it, is covered in stopping multi-color paint from bleeding past your edges. You want both: a sharp edge on the model, and enough purge at the swap to honor it.
Step 1 — Read the swap count in Layerpaint first
Before you touch the slicer, open your model in the painter and turn on Show swap bar in the Layers panel. The bar counts total filament swaps and shows where they stack up by layer. A high count means you'll be flushing a lot, so the per-swap volume matters more.
The Flush volume field next to it is an estimate, not a control. It multiplies your swap count to show roughly how much filament the job will burn. Set it near whatever your slicer actually uses and you'll get a realistic waste figure. If the count looks brutal, reorder your palette before exporting; reordering the palette cuts swaps before flush volume even enters the picture.
Step 2 — Print the flush test with volumes at zero
Grab a flush calibration model. The community ones on MakerWorld and Printables print a stack of color transitions for two or four filaments. Load it in OrcaSlicer or Bambu Studio, assign the same filaments you'll print your real model with, and set every flushing volume to 0 so nothing is masked. Slice and print.
The test prints each color change as a band. With zero purge, the start of each band carries streaks of the previous color, and somewhere up the band it goes fully clean.
Use the actual filaments from your AMS, MMU, or CFS, not stand-ins. A matte dark filament bleeding into a light one needs far more purge than two similar mids, so testing the wrong pair gives you a number you can't trust.
Step 3 — Read where each transition goes clean
Look at each band and find the height where the new color stops carrying any of the old one. The model is marked with volume values along its height, so the mark at that clean point is your required flush for that pair. Add roughly 20 mm³ on top as a buffer for filament and nozzle variation.
Direction matters. Dark into light needs the most purge, because any leftover dark shows. Light into dark needs less, since traces of the lighter color disappear. So the from/to pair isn't symmetric, and you'll record a different number each way.
Step 4 — Enter the values in the Flushing volumes table
In OrcaSlicer or Bambu Studio, find the Flushing volumes button in the project filament panel and open the table. It's a grid of every from → to color pair, with a global Multiplier above it. Reset the multiplier to 1.00 so it isn't scaling your work, then type each calibrated value into its cell. The lighter-to-darker cells go lower than the darker-to-lighter ones, matching what you saw on the test.
If you'd rather not redirect the purge into a tower, that's a separate setting: flush into objects and infill hides most of it inside the part. Calibrated volumes and flush into infill stack: dial the volume down here, then route what's left into the model.
Step 5 — Reslice and confirm the boundaries
Reslice your painted 3MF with the new table and check the sliced preview's filament-usage estimate; it should drop from the default. Then print the real part. The boundaries you painted should now come through with the bleed gone and noticeably less in the purge tower.
Save the values into the filament profile so you don't redo this every project. The flush table travels with the model file, so a fresh import can fall back to defaults if you skip this.
Common questions
Does Layerpaint set the flushing volume in the exported 3MF?
No. Layerpaint paints the colors and exports a Standard 3MF; flushing volumes are a slicer setting you tune after import. The Flush volume field in the Layers panel is only an estimate that feeds the waste readout on the swap bar. It doesn't change the exported file.
Will lower flushing volumes cause color bleed?
Below the calibrated number, yes. That's the whole point of testing rather than guessing. At or just above the clean-transition value you found, the boundary stays sharp. The buffer exists so normal print-to-print variation doesn't push you back under the line.
Do I have to recalibrate for every filament set?
Recalibrate when you change a filament's color or finish. A matte black behaves differently from a silk black, and a brand-new pairing you haven't tested is a guess. Same filaments in a different palette order are fine. Only the from/to relationships you actually print need numbers.
Does this work for Prusa MMU3 and the Anycubic ACE Pro or Creality CFS?
The idea is universal: every multi-filament system purges on a swap. PrusaSlicer has its own Purging volumes dialog under the wipe-tower settings, with the same from/to grid, and the OrcaSlicer-based slicers for the ACE Pro and CFS carry the same Flushing volumes table as OrcaSlicer.
Try it now
Layerpaint is free to try — no account, no install, no upload. Paint your model on the painter, watch the swap bar, and export when you're ready. A one-time payment of $19.97 unlocks 3MF export forever. No subscription.
Happy printing. 🎨