TL;DR: If the Flushing Volumes matrix in Bambu Studio shows 0 everywhere and Re-calculate won't repopulate it, look at the Multiplier field in that same dialog. It's sitting at 0.00, and every computed volume gets multiplied by it. Set the flush multiplier to 1.00, click Re-calculate, and reslice. Two different Bambu forum threads confirmed this exact fix. Below are the five steps and what to do if colors still bleed afterward.
Why are my flushing volumes all 0?
Bambu Studio multiplies every value in the Flushing Volumes matrix by the Multiplier field at the bottom of the same dialog. When that field reads 0.00, every computed volume becomes zero, so the printer barely purges between color changes and the previous filament contaminates the next one. Re-calculate looks broken because the calculation runs and then gets multiplied by zero. Setting the flush multiplier back to 1.00 and clicking Re-calculate restores normal values immediately.
The nasty part of this bug is that there's no error message. The print starts, the AMS swaps filament on cue, and the result looks like a purge problem: a whole layer tinted the wrong shade, or colors that muddy into each other at every transition. Users on the Bambu Lab forum describe exactly that: colors not in the right places, not enough filament flushed between changes.
The multiplier can end up at 0.00 without you ever touching it. The user who reported it, Jek, put it plainly after finding the fix: "That is so weird how it just changed without me changing it." There's a matching report on GitHub, Flush Multiplier & Values Ignored at 0, so it's a known quirk, not something you broke.
Step 1 — Open the Flushing Volumes dialog
In Bambu Studio's Prepare view, find the filament list on the left and click the Flushing volumes button next to it. The dialog shows a matrix: one row per loaded filament, one column per filament it can change into, each cell holding the purge volume in mm³ for that transition.
Step 2 — Check the Multiplier field
Look below the matrix. There's a small box labeled Multiplier. On a healthy setup it reads 1.00. If yours shows 0.00, you've found the whole problem: every cell in the matrix is being multiplied into nothing. This is the flush multiplier bug, and no amount of clicking Re-calculate will fix it while that field stays at zero.
Step 3 — Set the flush multiplier to 1.00
Click into the box and type 1.00. That's the default. Values above 1.00 purge more per transition, values below purge less. You can tune it later; right now the job is getting off zero.
Step 4 — Click Re-calculate
Now hit Re-calculate. The matrix fills in with real numbers based on your filament colors. Transitions from dark to light get the biggest volumes, because a trace of black left in the nozzle shows up badly in white. If the cells populate, the fix has worked.
Step 5 — Reslice and check the preview
Reslice the plate. In the sliced preview, switch the view to Filament and check the prime tower: you should see solid purge blocks at each color change again. Send the print. On the forum thread where JonRaymond first pointed at the multiplier, OP Jek came back with "it is fixed now thank you," and in a second, unrelated thread the same fix got the same result: "Thanks a lot…it works."
Before any long multicolor job, glance at the Multiplier box whenever you open Flushing Volumes. It's a two-second check, and it's cheaper than discovering a zeroed matrix four hours into an eight-color print.
If colors still bleed after the fix
A restored matrix gets you back to Bambu Studio's computed defaults. Those defaults are decent, not perfect. If your dark-to-light transitions still carry a tint, that's a calibration job, not a bug: work through calibrating flushing volumes for a painted 3MF to set per-pair values that match your actual filaments.
And if your complaint is the opposite, too much purge waste, don't fix it by dragging the flush multiplier toward zero. Reordering your palette cuts swaps without touching purge volumes, and flushing into infill reuses waste filament inside the model where it can't be seen.
This matters double for painted models. A 3MF painted in Layerpaint can put six or eight colors on one plate, which means dozens of transitions in the matrix. Turn on the swap bar in the painter and you can see the color-change count before you export, and every one of those changes relies on a sane flush multiplier once the file reaches Bambu Studio.
Common questions
Does the flush multiplier bug affect OrcaSlicer too?
OrcaSlicer has the same Flushing Volumes dialog with the same multiplier field, so the same ten-second check applies. The confirmed reports above are all from Bambu Studio, but if your Orca matrix reads 0 everywhere, look at the multiplier before anything else.
What's a normal flush multiplier value?
1.00 is the default and the right starting point. Some people drop to 0.6 or 0.8 after calibrating per-pair volumes to reduce waste, and push above 1.00 for stubborn pairs like red into white. Zero is never a valid setting.
Why did my multiplier change to 0 by itself?
Nobody has pinned down the trigger. The GitHub issue tracking it has reports of the value resetting between sessions, and the forum reports say the same. Until it's patched, treat the Multiplier box as something to verify rather than something to trust.
Will setting it back to 1.00 waste more filament?
It restores the volumes Bambu Studio calculated from your filament colors, which is what the printer needed all along. If the waste bothers you, cut it with palette order and infill flushing rather than by shrinking the multiplier below what your colors can tolerate.
Try it now
Layerpaint paints STL, OBJ, and 3MF models right in your browser and exports a Standard 3MF that Bambu Studio opens with every color group intact. There's nothing to install, and your mesh never leaves your device. Drop a model on the painter and see the swap count before you ever slice. Your first export is free, then $2.97 for your next 3 models or $39.97 unlimited. No subscription.