Multi-Color and Multi-Material Prints

Two different jobs

Decide first which kind of multi-color print you need, because the hardware and the waste are very different.

	Color change at a layer	Automatic filament changes
Colors can change	Only between layers (bands by height)	Within a layer, anywhere
Hardware	Any printer that supports a pause or filament change command	A filament changer feeding one nozzle, or several nozzles or tools
You	Swap the spool by hand at each change	Nothing, once it is set up
Waste	A short purge at each manual change	A purge at every change, often many per layer

The hardware side (filament changers, toolchangers and how each handles purging) is in Multi-Material Systems and Purge Waste. This page is about planning the print.

Color change at a layer

Lettering on a sign, a two-tone coaster or a striped vase only need colors by height. PrusaSlicer describes adding a color change from the layer slider in the sliced preview; the printer pauses when it reads the color change command (M600) in the G-code, and you load the next filament. Prusa says this can be used for basic multicolored models. Other slicers have the same feature on their layer slider.

• Design the color boundaries at a flat height so they land on a layer.
• Check the change sits on the right layer in the preview before printing.
• Be at the printer when the change comes up, and keep hands clear of the hot nozzle while swapping.

Where the waste comes from in automatic changes

Bambu Lab's guide breaks a filament change into stages. Each one costs plastic or time:

• Flushing (purging). Old filament left in the nozzle is pushed out until the new color comes out clean. Bambu notes the volume depends mainly on the color pair: dark to light needs more than light to dark. Support filaments get extra flushing so they do not contaminate the part and stick to it.
• Priming. The nozzle then prints into a prime tower, a sacrificial block beside the part, so the next line on the real part starts with steady flow.
• The tower grows with the print. The prime tower must reach the highest layer with a change. Bambu's example rotated a part so all its color changes sat near the bottom, and the tower dropped from 14.76 g to 9.05 g, about 40 percent less Measure it.

Ways to cut waste

Bambu Lab points out that waste follows the number of filament changes. In almost every case, a layer needs one fewer change than the number of filaments on it Rule of thumb, because the slicer starts each layer with the last color of the layer below.

1. Fewer layers. A thicker layer height means fewer layers and so fewer changes. In Bambu's example, going from 0.2 to 0.28 mm cut changes from 153 to 111 and waste from 83 g to 61 g Measure it. See Choosing a Layer Height for what you give up.
2. Orientation. If colors run in vertical stripes, laying the part on its side can stack the colors by layer instead. Bambu's example cut changes and waste by almost 80 percent this way. It also gives the opposite example: a part already colored in horizontal bands got 22 times more waste when laid down. Slice both ways and compare the filament totals. See Print Orientation.
3. Flush into infill. The purge goes into the part's hidden infill. Bambu and OrcaSlicer both warn that light or transparent walls can show the mixed color through, and Bambu adds that fewer walls make that more likely.
4. Flush into supports. Supports are thrown away anyway. Bambu enables this by default; it helps most on prints with a lot of support.
5. Flush into an object. Mark another object on the plate, such as a functional part you will paint, to be printed from purge plastic. Its color will be mixed. Bambu suggests making these parts about the same height as the multi-color part.
6. Lower flushing volumes, carefully. Bambu Studio's flushing multiplier defaults to 1.00. Bambu says the defaults lean high for quality and that 0.8 or 0.9 can save filament Starting point, but too low shows up as discolored layers, so test.

OrcaSlicer notes that the flush into infill, support and object options only work with the prime tower enabled, and Bambu Lab says the same for flushing into supports.

Soluble and breakaway supports

The same filament-change machinery lets you print supports in a different material, such as a water-soluble one, so they come off cleanly from complex shapes. The material choices and how to dissolve them are in Soluble Supports: PVA and BVOH. Expect larger flushing volumes at the support interface, for the contamination reason above.

Preparing the model

• Prusa's design guide says that for multi-material printing each part must be manifold and solid. Model each color as its own closed body, or paint colors in the slicer if it has a painting tool.
• Very thin slivers of one color take a full change for little plastic. Merge tiny details into a neighbor color where you can.
• Compare the slicer's estimate of filament used, number of changes and time before printing. Those three numbers tell you how much each choice above saved.