You download a multi-colour project from MakerWorld or from a generator, open it on your new H2C or H2D, press Slice, and Bambu Studio stops with: “Error: Purge volumes matrix do not match to the correct size!” The model looks fine, the filaments are there, nothing is obviously wrong. The error message is unhelpful, but the cause is simple, and the fix takes two minutes.
We hit it ourselves twice this autumn, both times reported by H2C owners, so this post is as much a note to ourselves as a guide.
What the matrix is
Every Bambu Studio project stores a table of purge volumes: how much filament to flush when switching from colour A to colour B, for every pair of filaments. With four filaments that is a 4 by 4 table, sixteen numbers. The slicer needs the table to match the number of filament slots in the project exactly.
A dual-nozzle printer (H2C, H2D, H2S) adds a second dimension: the table also depends on which nozzle each filament lives in. A project saved from a single-nozzle printer carries a table of the wrong shape for a dual-nozzle machine. When Bambu Studio sees a table that does not fit the printer profile, it refuses to slice rather than guess.
Why downloaded projects trigger it
Almost every multi-colour 3MF on MakerWorld was saved on an A1, P1 or X1, so the stored table is the single-nozzle one. Bambu Studio can usually rebuild it, but not when the table and the filament list disagree about how many slots there are. That was exactly our bug: a project with four filaments carrying a table sized for five. The H2 profile checks the table more strictly than the single-nozzle profiles, so the same file slices on a P1 and fails on an H2C.
Fix 1: reset the flushing volumes in the project
- Open the project and select your H2 printer in the printer dropdown if it is not already selected.
- Click the “Flushing volumes” button above the filament list (the icon with two arrows).
- In the dialog click “Re-calculate” (or “Reset” on older versions) and confirm. Bambu Studio rebuilds the table for the current printer and filament count.
- Slice again.
Fix 2: let the generator build the project for your printer
If the file comes from a generator, the cleanest fix is upstream. In the TanskyLab generator pick your printer under the bed size (“H2C” or “H2D / H2S”) before you download. The project then leaves out the single-nozzle purge table altogether and Bambu Studio calculates it from your printer profile, so the error cannot occur. This is also what sets the correct bed size for the plate split.
Full disclosure: between 4 and 9 October 2026 our H2C and H2D projects carried a trimmed filament table and triggered this exact error. That is fixed; if you generated a file in that window, generate it again.
Fix 3: import geometry, then add colours by hand
The brute-force route for models that will not cooperate: File, Import, “Import geometry only”, which drops every project setting including the broken table. You lose the colour changes, so you have to add them back in the Preview tab at the heights the model author lists. For a photo puzzle that is three or four heights, written in the generator next to each filament.
Things that do not fix it
- Changing the nozzle size or the filament type. The table shape depends on the filament count and the printer, not on the material.
- Deleting a filament to “make room”. The relief needs every colour; you get a different error later.
- Re-downloading the same file. The table is inside the file; it will not change until the project is rebuilt.
If the model slices but shows up all black in the Prepare view, that is a different and harmless thing: see why multi-colour prints look black before slicing.