What does purge or flushing mean?
In a single-nozzle multi-material system, some of the previous filament remains in the melt zone after a change. Purge/Flushing is the controlled extrusion used to remove that remainder until the new color or polymer is sufficiently clean.
Why purge is directional
Black-to-white usually needs more cleaning than white-to-black. Two different polymers can also behave very differently from two colors of the same material. A directional flush matrix is therefore more useful than one global number.
Too little vs. too much
Too little purge can create color contamination, weak transition zones or problematic mixing of incompatible polymers. Too much increases waste and print time without improving the part. The target is the lowest reliably sufficient amount, not simply the smallest number.
Where can purge material go?
A slicer may send transition material to waste, a purge structure or a prime tower. OrcaSlicer can also redirect some purge into object infill or support. This can reduce external waste, but mixed colors may show through light or transparent walls and mixed polymers may be inappropriate in functional regions.
Flush into Infill is not free purge
The required transition volume has not disappeared; it is only being used somewhere inside the print. Do not reduce the required purge again simply because it is redirected to infill.
Practical workflow
- Reduce unnecessary material changes in the model first.
- Evaluate transitions as directional pairs.
- Validate difficult color/material combinations with a small test.
- Only then optimize Flush into Infill/Support and the prime tower.
For prints with many changes, reducing the number of transitions can have a larger effect than aggressively cutting every purge volume.