What flushing volume should you use? Values by color pair

Use the flushing volume your slicer calculates for each color pair, at a multiplier of 1.0. Bambu Studio and OrcaSlicer set black to white at 667 mm³ (0.83 g of PLA, polylactic acid) and white to black at 187 mm³ (0.23 g) on an X1 Carbon or P1S profile. Lower that only after a test print shows clean color changes.

What flushing volume should you use?

Use the per-pair values Bambu Studio or OrcaSlicer calculate from your filament colors, unchanged at first. On an X1 Carbon or P1S profile, light to dark changes land around 130 to 300 mm³ and dark to light changes around 420 to 725 mm³. The flat 280 mm³ in the default settings is only a fallback.

The slicer fills the table on its own when you assign filaments, so you rarely type these numbers. What you choose is the multiplier, which scales every pair.

Bambu Studio’s default is 1.0, and the field accepts 0 to 3. Bambu Lab’s wiki says the automatic values “tend to be slightly higher than necessary” and suggests 0.8 or 0.9 as a first saving, checked with a test print. At 0.8, black to white drops from 667 to 534 mm³.

How much flushing volume does a black to white change need?

Bambu Studio and OrcaSlicer give pure black (#000000) to pure white (#FFFFFF) 667 mm³ on an X1 Carbon or P1S profile. That is a 560 mm³ color score plus the printer’s 107 mm³ nozzle volume. In PLA at 1.24 g/cm³, one change flushes about 0.83 g, one of the costliest pairs.

The printer profile moves the number a little. The A1 profile lists a 92 mm³ nozzle volume, so black to white comes to 652 mm³.

Bambu’s own PLA Basic profile also turns on an 18 mm long retraction when the filament is cut. The slicer subtracts those 18 mm of 1.75 mm filament (about 43 mm³) from the nozzle volume. That brings black to white on an X1 Carbon to 623 mm³.

Prusa’s knowledge base gives far smaller example values for its MMU (Multi-Material Unit): 150 mm³ black to white. The MMU sums an unload and a load volume per filament, so do not copy those numbers into Bambu Studio or OrcaSlicer.

How much flushing volume does white to black need?

187 mm³, or 0.23 g of PLA, on the same X1 Carbon or P1S profile: an 80 mm³ color score plus the 107 mm³ nozzle volume. That is just over a quarter of the black to white figure. Prusa’s MMU example runs the same way at 50 mm³ white to black.

Flushing volumes table by color pair

These are the values Bambu Studio and OrcaSlicer put in the table for these hex colors, at a multiplier of 1.0 and a 107 mm³ nozzle volume, with no long retraction. The colors are the ones in the slicers’ own measured reference data, plus pure white. Grams are for PLA at 1.24 g/cm³ and use the Bambu Studio figure.

From → To	Bambu Studio	OrcaSlicer	PLA per change
Blue #0A2989 → Yellow #F4EE2A	725 mm³	673 mm³	0.90 g
Black #000000 → White #FFFFFF	667 mm³	667 mm³	0.83 g
Blue #0A2989 → White #FFFFFF	666 mm³	666 mm³	0.83 g
Red #C12E1F → White #FFFFFF	611 mm³	611 mm³	0.76 g
Black #000000 → Light gray #D1D3D5	598 mm³	598 mm³	0.74 g
Green #00AE42 → White #FFFFFF	582 mm³	582 mm³	0.72 g
Orange #FF6A13 → White #FFFFFF	570 mm³	570 mm³	0.71 g
Black #000000 → Yellow #F4EE2A	557 mm³	493 mm³	0.69 g
Black #000000 → Gray #8E9089	483 mm³	483 mm³	0.60 g
Black #000000 → Red #C12E1F	469 mm³	469 mm³	0.58 g
Gray #8E9089 → White #FFFFFF	425 mm³	425 mm³	0.53 g
Black #000000 → Dark gray #545454	364 mm³	343 mm³	0.45 g
White #FFFFFF → Green #00AE42	290 mm³	290 mm³	0.36 g
White #FFFFFF → Red #C12E1F	285 mm³	285 mm³	0.35 g
White #FFFFFF → Blue #0A2989	265 mm³	265 mm³	0.33 g
Yellow #F4EE2A → Black #000000	227 mm³	163 mm³	0.28 g
White #FFFFFF → Black #000000	187 mm³	187 mm³	0.23 g
Red #C12E1F → Black #000000	182 mm³	133 mm³	0.23 g
White #FFFFFF → Gray #8E9089	167 mm³	167 mm³	0.21 g
Same color in two slots	167 mm³	167 mm³	0.21 g

The two slicers part ways only where a pair sits in their measured reference data, which Bambu Lab and the OrcaSlicer project maintain as separate files. Your own shades will shift these numbers, so read your table rather than copying a row. To price a whole print, put your average flush per change into the multi-color waste calculator.

Why does dark to light need more flush than light to dark?

A trace of dark pigment shows up in a light color, while a trace of light pigment vanishes in a dark one. The source code builds that in. Its comments state that a color difference “is more obvious if the dest color has high luminance” and “if the source color has low luminance.”

The brightness term gets a weight of 560 when the change goes toward a lighter color and 80 when it goes toward a darker one, seven times less. Only the lighter-going term is raised to the 0.7 power, which inflates small brightness gaps. Going darker, the hue term is also capped by how bright the new color is, so a dark target hides hue differences as well.

Bambu Lab’s wiki puts it the same way: “Darker colors need a higher volume flush to switch to lighter colors.” Prusa’s knowledge base blames the “higher color contamination from a darker to a lighter color.”

How do Bambu Studio and OrcaSlicer calculate flushing volume?

Both use the same formula in FlushVolCalc.cpp. The slicer first checks whether both colors closely match two of its 12 reference colors (a CIEDE2000 difference of 5 or less) and the pair has a measured score in its data file. If so, it uses that score. If not, it uses this formula:

brightness  = 0.3 R + 0.59 G + 0.11 B        (R, G, B from 0 to 1)
to lighter:   L = (brightness change)^0.7 × 560
to darker:    L = brightness change × 80
hue term:     H = 230 × hue and saturation distance (distance capped at 1.2)
color score = √(L² + H² + L × H), never below 60
flush mm³   = color score + nozzle volume, capped at 900 in Bambu Studio
PLA grams   = flush mm³ × 1.24 ÷ 1000

Worked example, black to white: brightness rises from 0 to 1, so L = 1^0.7 × 560 = 560. Neither color has any saturation, so H = 0. The score is √(560²) = 560. Add the 107 mm³ nozzle volume to get 667 mm³, and 667 × 1.24 ÷ 1000 gives 0.83 g.

The limits and fixed values

Rule	Value	Where it comes from
Smallest color score	60 mm³	FlushVolCalc.cpp; with the nozzle volume, 167 mm³ on an X1 Carbon
Largest flush per pair	900 mm³ (Bambu Studio), 20,000 mm³ (OrcaSlicer)	FlushVolCalc.cpp
Change into a support filament	230 mm³	FlushVolCalc.cpp
Change out of a support filament	at least 700 mm³	FlushVolCalc.cpp
PLA Basic ↔ PETG Basic	at least 650 mm³	Bambu Studio’s measured material pair file
Before colors are assigned	280 mm³	PrintConfig.cpp default matrix
Multiplier	1.0 default, 0 to 3	PrintConfig.cpp, WipeTowerDialog.cpp

A transparent filament counts as white. A multicolor spool takes the highest value among its colors.

What happens if the flushing volume is too low?

The old color bleeds into the new one. Bambu Lab’s wiki says a value set too low “will show as discolored layers”: a tint where one color meets the next. Print a short test with the pairs your model uses, then raise only the pairs that bleed. Prusa’s knowledge base adds that glossy, glitter or soluble filaments usually need more purge than standard values.