Flushing volume multiplier: what it does and what to set

The flushing volume multiplier scales every value in the slicer’s flushing volumes table, so at 0.8 the printer purges 20% less plastic at every color change. Bambu Studio defaults it to 1.00, and Bambu Lab’s wiki suggests 0.8 or 0.9 as a quick saving once a test print shows no color bleed. Set it too low and the old color shows up as tinted layers in the new one.

What is the flushing volume multiplier?

The flushing volume multiplier is one number that scales every cell of the slicer’s flushing volumes table. At each filament change the slicer purges the table value times the multiplier, so 0.8 flushes 20% less on every color pair. Bambu Studio defaults it to 1.00 and accepts values from 0 to 3.

The table holds one flush volume in mm³ for each from/to pair of filaments. Bambu Studio and OrcaSlicer calculate each cell from the two colors, then apply the multiplier to the whole table:

flush per change (mm³) = table cell × multiplier       (rounded to a whole mm³)
grams per change       = flush mm³ × density g/cm³ ÷ 1000

Bambu Studio’s tooltip puts it this way: “The actual flushing volumes is equal to the flush multiplier multiplied by the flushing volumes in the table.” OrcaSlicer’s GCode.cpp does the same, multiplying each cell and rounding it. A few details follow from that:

• The cut is proportional. A dark-to-light pair at 500 mm³ loses 100 mm³ at 0.8, while a light-to-dark pair at 150 mm³ loses 30 mm³. You can’t use the multiplier to cut only the expensive pairs. To do that, edit single cells.
• It survives recalculation. Bambu Studio recalculates the table whenever a filament or its color changes, and the multiplier stays applied on top.
• It doesn’t touch the prime tower. The tower’s prime volume is a separate setting (45 mm³ per change by default in OrcaSlicer).

What is the default flushing volume multiplier in Bambu Studio and OrcaSlicer?

Slicer	Default in source	Range in the flushing dialog
Bambu Studio	1.00	0 to 3
OrcaSlicer	0.3 fallback in PrintConfig.cpp	0 to 3

Bambu Lab’s wiki confirms 1.00 as the Bambu Studio default and calls 0.90 “10% less flushing volume for every filament change pair.” OrcaSlicer’s source sets a fallback of 0.3, but its flushing dialog code treats 1 as the unmodified value when it flags a changed table. Open the dialog and read the number your project uses before you compare settings with someone else.

Bambu Studio’s dialog also suggests keeping each cell between 0 and 700 mm³. On printers with two nozzles, each nozzle has its own multiplier. A separate fast-mode multiplier, defaulting to 1.2, applies only when the purge mode is set to Fast.

How much does lowering the multiplier save?

Take OrcaSlicer’s default 280 mm³ flush between two different filaments, PLA (polylactic acid) at 1.24 g/cm³ and 12 mm³/s max volumetric speed (both from OrcaSlicer’s PLA profile), and an assumed spool price of $20 per kg. Say your print has 300 color changes:

grams per change at 1.0 = 280 × 1.24 ÷ 1000            = 0.347 g
grams per change at 0.8 = 224 × 1.24 ÷ 1000            = 0.278 g
grams saved             = 300 × (0.347 − 0.278)        = 20.8 g
dollars saved           = 20.8 × 20 ÷ 1000             = $0.42
flush time saved        = 300 × (280 − 224) ÷ 12 s     = 23 min

Multiplier	Flush per change	Waste, 300 changes	Saved vs 1.0	Waste, 1,000 changes	Saved vs 1.0
1.0	280 mm³	104.2 g ($2.08)		347.2 g ($6.94)
0.9	252 mm³	93.7 g ($1.87)	10.4 g, $0.21, 12 min	312.5 g ($6.25)	34.7 g, $0.69, 39 min
0.8	224 mm³	83.3 g ($1.67)	20.8 g, $0.42, 23 min	277.8 g ($5.56)	69.4 g, $1.39, 78 min
0.7	196 mm³	72.9 g ($1.46)	31.2 g, $0.62, 35 min	243.0 g ($4.86)	104.2 g, $2.08, 1 h 57 min

The time column counts flush time only, since unload and load time per change stays the same. Per print the money is small. The time and grams add up across a busy plate or a run of prints.

Your own table won’t be a flat 280 mm³, but the percentage holds: 0.8 removes 20% of the flush whatever the cells contain. Enter your change count, average flush and spool price in the multi-color waste calculator to see the grams and hours for your own model.

What flushing volume multiplier should you use?

Keep 1.0 until a test print says otherwise, then try 0.8 or 0.9, the quick saving Bambu Lab’s wiki suggests. One published black-to-white test went as low as 0.46 without visible bleed. Your worst color pair sets the floor: dark-to-light changes and glossy or glitter filaments need more flush.

Bambu Lab’s wiki explains why there’s room to cut: the default values “tend to be slightly higher than necessary in order to err on the side of print quality.” How far you can go depends on four things:

• The worst pair on the plate. One multiplier scales every pair, so the pair that needs the most flush decides the floor. In the color formula in OrcaSlicer’s source, pure black to pure white scores 560 mm³ before the minimum flush is added, while white to black scores 80 mm³. Prusa’s MMU (Multi-Material Unit) example points the same way: 150 mm³ black to white, 50 mm³ white to black.
• The filament. Prusa’s knowledge base says soluble supports and filaments with additives (“highly glossy, glitter, etc.”) most likely need more purging. OrcaSlicer calculates a transparent filament as if it were white.
• Where the color shows. Bleed on an outer wall is visible. Bleed in hidden infill or on a part you’ll paint is not, so those prints tolerate a lower multiplier.
• The slicer version. The test that reached 0.46 (GuyH on Printables) used Bambu Studio 1.1 and its tables of the time, with no prime tower. 0.42 already showed slight bleed and 0.33 clear bleed. A newer version can calculate different cells, so treat 0.46 as that test’s result, not a target.

In practice: 0.8 to 0.9 is the low-risk step, about 0.5 is near the floor one documented worst-case test reached, and values above 1.0 are for pairs that still bleed at the default.

What happens if the multiplier is too low?

The old color doesn’t clear the nozzle before the new one starts printing. Bambu Lab’s wiki describes the result as “discolored layers”: a light color tinted by the dark one it follows. A multiplier near 0 removes the flush almost entirely, so every change prints mixed color into the part.

How do you find your lowest safe multiplier?

1. Load the filaments you print with and let the slicer calculate the table at 1.0.
2. Print a small two-color test that runs your worst pair, usually your darkest filament into your lightest. GuyH’s test alternated white, black, white across thin layers.
3. Step the multiplier down by 0.1 and reprint: 0.9, then 0.8, then 0.7.
4. Stop at the first print with any tint where the light color follows the dark one. Go back to the last clean value. GuyH kept a prime tower on his real prints as a margin for error.
5. Re-test when you change filament brand, add a transparent or glitter filament, or update the slicer.

If only one pair bleeds, raise that pair’s cell in the table instead of the whole multiplier. For more ways to cut purge waste, such as fewer changes, thicker layers and flushing into infill, see whether multi-color printing is worth the filament cost.