Flushing volume from PLA to PETG and back

Plan on about 650 mm³ of flush per change between PLA (polylactic acid) and PETG (polyethylene terephthalate glycol), in either direction. That is about 0.8 g per change. Bambu Studio applies that figure to Bambu PLA Basic and Bambu PETG Basic from its own measured test data. For any other PLA and PETG pair, Bambu Studio and OrcaSlicer calculate the flush from color alone, so a same-color material change gets far less flush than it needs.

How much flushing volume do you need between PLA and PETG?

Bambu Studio sets at least 650 mm³ per change between Bambu PLA Basic and Bambu PETG Basic, in both directions, from Bambu Lab’s measured purge table. That is about 0.83 g of PETG or 0.81 g of PLA. Other PLA and PETG pairs get only a color-based value, so set them to 650 mm³ yourself and test.

What each slicer puts in the flushing volumes table for a PLA and PETG change:

Slicer and filaments	Flush per change
Bambu Studio, Bambu PLA Basic to or from Bambu PETG Basic	650 mm³, or the color value if that is higher
Bambu Studio, any other PLA and PETG pair (PETG HF, third-party filament)	Color value only
OrcaSlicer, any PLA and PETG pair	Color value only; 280 mm³ default when not auto-calculated
Either slicer, changing into a filament flagged as support	230 mm³ fixed
Either slicer, changing out of a filament flagged as support	At least 700 mm³

The 650 mm³ entry sits in Bambu Studio’s flush_data_material_pair.json. It was added in June 2026 and ships with Bambu Studio 02.08 and later. The file lists only four pairs. The other two are ABS to PA6-GF at 400 mm³ and ASA to PAHT-CF at 350 mm³.

Does the slicer flush volume account for material or only color?

Mostly only color. In OrcaSlicer’s FlushVolCalc.cpp, the flush function takes the two filament colors and nothing else. A transparent filament counts as white.

The result is a color distance plus a minimum flush. In Bambu Studio that minimum is the nozzle volume, 107 mm³ in the X1 Carbon 0.4 mm profile. A white PLA to white PETG change is therefore priced like a white to white change within one material.

Bambu Studio’s version of the same file adds one material step. It also looks up the two filament IDs in the measured table and keeps whichever value is larger. Bambu Lab’s wiki says color is the main factor and material properties come second. Its example is support filament, where the flush prevents “contamination which would cause sticking between a support filament and the filament it supports.”

The only other material rule in either slicer applies to filaments flagged as support, such as Bambu Support for PLA/PETG. A change into one gets a fixed 230 mm³, and a change out of one gets at least 700 mm³. Plain PLA and plain PETG don’t carry that flag.

Why leftover PETG spoils PLA layers, and the reverse

The two plastics print 35 °C apart in Bambu’s X1 Carbon profiles and don’t bond well to each other. Bambu Lab’s mutual-support guide says that weak bond is why each makes a good support interface for the other. The same weak bond causes the trouble when the flush runs short:

• PLA left in a PETG interface fuses the interface to the PLA model, so the support no longer snaps off cleanly.
• PETG left in a PLA part leaves streaks that bond poorly to the surrounding PLA.

	Bambu PLA Basic	Bambu PETG Basic / PETG HF
Nozzle range (data sheet)	190 to 230 °C	230 to 260 °C
Print temperature (X1 Carbon profile)	220 °C	255 °C (PETG Basic)
Flush temperature (X1 Carbon change G-code)	240 °C	260 °C

The X1 Carbon’s filament change G-code heats the nozzle to a flush temperature for the incoming filament, which the code comments call “always use highest temperature to flush.” For PETG it hard-codes 260 °C. For PLA it uses the profile’s top limit of 240 °C.

After a PETG to PLA change, the PETG still in the nozzle is flushed at 240 °C, and the PLA layer then prints at 220 °C. Both are below PETG’s 255 °C print setting.

How many grams does a PLA to PETG change waste?

About 0.83 g at 650 mm³, because the flush is the incoming PETG. The PETG to PLA change flushes PLA, about 0.81 g.

grams per change = flush mm³ × density g/cm³ ÷ 1000
PLA to PETG:  650 × 1.27 ÷ 1000 = 0.83 g of PETG
PETG to PLA:  650 × 1.24 ÷ 1000 = 0.81 g of PLA

Densities are OrcaSlicer’s generic profiles: PLA 1.24 g/cm³ and PETG 1.27 g/cm³. Bambu’s data sheets give 1.25 for PETG Basic and 1.28 for PETG HF, which moves these figures by about 0.01 g.

Flush per change	PETG (1.27 g/cm³)	PLA (1.24 g/cm³)
280 mm³ (OrcaSlicer default)	0.36 g	0.35 g
650 mm³ (Bambu Studio measured pair)	0.83 g	0.81 g
900 mm³ (Bambu Studio maximum per entry)	1.14 g	1.12 g

Worked example. Say a PLA part with a PETG support interface slices to 30 filament changes, 15 each way. At 650 mm³: 15 × 0.83 + 15 × 0.81 = 24.5 g of flush. At OrcaSlicer’s 280 mm³ default it would be 10.5 g, well under what Bambu measured for this pair. Enter your own change count and flush in the multi-color waste calculator to get the cost and added time.

How to raise the flush volume for a PLA to PETG change

1. Open the flushing volumes table in Bambu Studio or OrcaSlicer.
2. Edit only the two cells for the PLA and PETG pair: PLA to PETG and PETG to PLA. Start at 650 mm³. Bambu Studio caps each cell at 900 mm³. OrcaSlicer’s cap is 20,000 mm³.
3. Leave the multiplier at 1.0. It scales every pair, including color changes within one material. Both slicers accept 0 to 3.
4. In PrusaSlicer, edit the purging volumes matrix, or raise Purge Volume Multiplier under Filament Settings, Advanced on the PETG profile only.
5. Print a small test with the interface. If the support sticks to the part, or the part shows off-color streaks after a change, raise the flush for that direction and test again.

The Re-calculate button in Bambu Studio puts back the automatic values, including the 650 mm³ pair.

PETG as a support interface for PLA, and PLA for PETG

Bambu Lab’s guide to using each as the other’s support covers only Bambu PLA Basic with Bambu PETG HF or PETG Basic. It excludes PLA Matte, PLA Silk, PLA-CF, PETG Translucent, PETG-CF and all third-party PLA and PETG. Its settings:

• Use the second material for the support interface only, not the support base. A full base of the other material risks supports detaching and adds print time.
• PETG supporting PLA: PLA at 230 °C and PETG HF at 265 °C on all layers (PETG Basic at its default), with the PETG max volumetric speed at 10 mm³/s.
• PLA supporting PETG: PLA at 230 °C on all layers, PETG at its default.
• Bed at 60 °C on a smooth or textured PEI (polyetherimide) plate, with the door or top cover open on enclosed printers.
• Dry both filaments first. The guide warns that at PETG temperatures, moisture in PLA causes stringing and oozing.

The guide’s example was printed on a dual-nozzle printer, where each material stays in its own nozzle and the change is a nozzle switch instead of a flush. A PETG model with a PETG base and a PLA interface printed 1 h 20 min faster than one with all-PLA supports, and its purge tower used about half the filament. On a single-nozzle printer every interface layer adds a change, so keep the interface to as few layers as the part needs.