Multicolour 3D printing waste: how purge works and what it adds to the cost of a print

Where the waste comes from

Multicolour printers with one nozzle, which includes setups with Bambu Lab’s AMS, Creality’s CFS [6] and Anycubic’s ACE Pro [7], change colour by swapping filament. Bambu Lab explains that some old filament is left below the cutter each time; after the new filament is loaded, the extruder flushes the old one through the nozzle until only the new colour comes out [1]. That plastic is extruded next to the plate and directed away from the print [1]. On a P1S it drops out of a chute at the back, which is why Bambu Lab tells you to put a box under it [3].

Two things set how much is flushed. Colour is the main one: dark to light needs more than light to dark, because a little old colour shows as a stain [1]. Material matters too, especially for support filaments that must not contaminate the part [1]. After flushing, the nozzle prints on a prime tower by default, a sacrificial column that must be as tall as the highest colour change [1].

This page is about waste and cost. For choosing between Bambu Lab’s AMS and Creality’s CFS, see our comparison guide.

What Bambu Lab’s own examples show

Vendors do not publish a fixed grams-per-swap figure, because it depends on the colour pair. Bambu Lab does publish worked examples sliced in Bambu Studio, which give a realistic scale. In the cube example, waste works out to about 0.54 g per change. That is our arithmetic from one example, not a vendor specification.

Slicer settings that change waste

Bambu Studio calculates flushing volumes for every colour pair automatically and lets you scale them with a multiplier. Bambu Lab says the defaults err on the side of quality and that 0.8 or 0.9 could save filament, but only after a test print, because too little flushing shows as discoloured layers [1].

Three options redirect flushed plastic into something useful. Flush into objects’ infill uses it for hidden infill; Bambu Lab warns it can show through light, transparent or thin-walled parts [1]. Flush into objects’ support is on by default in Bambu Studio [1]. Flush into this object prints a whole sacrificial object with mixed colours [1]. OrcaSlicer documents the same three options and says none of them take effect unless the prime tower is enabled [2].

• Run a test at multiplier 0.9 before going lower.
• Use flush into infill only on dark, opaque parts with enough walls.
• Keep supports on the flush path where you need supports anyway.
• Add a useful single-colour object, such as a functional clip, as a flush target.

Cost scenario 1: a four-colour keychain batch

Assumptions: a 4 mm thick keychain printed at 0.2 mm is 20 layers; the four colours appear on the top 8 layers, each needing 3 changes per layer, so about 24 changes; each keychain weighs 5 g; flush waste uses the 0.54 g per change from Bambu Lab’s cube example, about 13 g. The prime tower is left out because its size depends on the model; in Bambu Lab’s prime-tower example it used 9 to 15 g [1].

Filament prices from official stores on the day we checked: Bambu Lab lists PLA Basic at an MSRP of $14.99 for a 1 kg refill without a spool, or $17.99 with a spool [4], and Creality Hyper PLA was $19.99 per 1 kg on sale, down from $32.99 [5]. The refill and sale prices work out to 1.5 and 2.0 cents per gram.

Because waste depends on changes per layer, not on how many identical parts share those layers [1], ten keychains on one plate cost almost the same in flush as one.

Cost scenario 2: a two-colour sign

A sign shows how design changes waste more than any setting. Take a 3 mm base in one colour with 1 mm of lettering in a second colour, printed at 0.2 mm.

If the letters are raised on top of the base, every layer is one colour and there is a single change at the 3 mm mark: well under a gram at Bambu Lab’s example rate. If the letters are inlaid flush with the top surface, the top 5 layers each contain both colours and need about one change per layer, because the printer starts each new layer with the colour it finished on [1]. That is about 5 changes, or roughly 3 g, a few cents. Bambu Lab shows the same principle in reverse: a part with colours organised by height needed 3 changes and 10 g of waste, but laid on its side it needed 22 times as much [1].

Checklist before you press print

Bambu Lab advises comparing approaches by slicing and checking filament use rather than guessing [1]. Use the slicer’s filament summary for each option below.

• Check the colour-change count in the slicer preview.
• Try a thicker layer height if the part allows it.
• Rotate the part so colour changes happen in fewer layers.
• Fill the plate with identical copies if you need more than one.
• Group parts that share colours on one plate.
• Add a flush object or use flush into infill where it will not show.
• Lower the flushing multiplier only after a test.
• Remember multi-unit setups multiply colours, not efficiency: one Creality CFS handles four colours and 16 needs four units [6].

Sources & verification

Product details and prices can change. Check the linked provider before buying.

1. Bambu Lab Wiki: Reduce waste during filament change Accessed 30 Oct 2026
2. OrcaSlicer Wiki: Multimaterial flush options Accessed 30 Oct 2026
3. Bambu Lab Wiki: Unboxing P1S (includes P1S specification table) Accessed 30 Oct 2026
4. Bambu Lab US store: PLA Basic filament Accessed 30 Oct 2026
5. Creality store: Hyper Series PLA 1kg Accessed 30 Oct 2026
6. Creality store blog: K2 Plus and CFS FAQs Accessed 30 Oct 2026
7. Anycubic Wiki: Notes for ACE Pro Accessed 30 Oct 2026