Multi-Colour 3D Printing with an AMS: What It Costs and How to Design For It

Painting a printed part is slow, skilled work. Masking curves is fiddly, paint adds thickness that ruins fits, and the first scuff reveals a different colour underneath.

A multi-material system removes the problem entirely. The colour is in the plastic, all the way through. A scratch reveals more of the same colour. There's no paint to chip, no decal to peel, and no assembly step.

Our Bambu Lab P1S runs a four-spool AMS, which makes this routine rather than exotic. Here's how it actually works, what it costs, and the one design decision that determines whether your part is cheap or expensive.

How an AMS works

The Automatic Material System sits beside the printer holding four spools of filament, each on its own feed path into a hub.

When the slicer reaches a point where the colour changes, the printer:

1. Retracts the current filament back out of the hot end
2. Feeds the next filament forward through the shared path
3. Purges: extrudes waste until the old colour is completely flushed out
4. Resumes printing

The whole exchange is automatic and takes a few tens of seconds. On a part with a lot of colour transitions it can happen hundreds of times.

Step three is the one that matters commercially, and it's where all the cost comes from.

Why colour changes cost money

The hot end contains a small but non-trivial volume of molten plastic. To go from black to white cleanly, every trace of the black has to be pushed out first, otherwise the white starts grey and fades in over the next several centimetres of extrusion.

That flushed material is waste. It comes out as a purge tower, a "poop" chute, or into the infill of the part where it won't be seen, but either way you paid for it.

The swap also takes time. During the retract-feed-purge cycle the printer isn't building your part. Multiply by a few hundred swaps and it adds up to hours.

We price this openly: a multi-material job runs roughly +45% material and +35% machine time against the same part in one colour. The estimator applies exactly that when you tick the multi-material option, so the price you see already includes it.

The one design decision that matters

almost nobody knows before their first multi-colour quote, and it can change the price by several times over.

Cost scales with the number of colour changes, not the number of colours.

Consider two parts, both using four colours.

Part A has four horizontal bands, red at the bottom, then blue, then yellow, then green. The printer loads red and prints until the band is done. One swap to blue. One to yellow. One to green. Three swaps in the entire print. The multi-material surcharge is almost nothing.

Part B has a repeating four-colour pattern running up the whole height, so every layer contains all four colours. On a 100 mm part at 0.2 mm layers that's 500 layers, each needing up to four swaps. Around 2,000 swaps. The purge waste can exceed the mass of the part itself, and the print might take three times as long as a single-colour version.

Same four colours. Wildly different cost.

So: group your colours by height wherever the design allows. If a logo must appear halfway up in a contrasting colour, that's a couple of swaps and it's cheap. If the logo is repeated as a texture across the whole surface, it's expensive. Knowing this at the design stage lets you get most of the visual effect for a fraction of the price.

A related trick: put contrasting details on a single face at a single height rather than distributing them. A control panel with all its coloured legends on the top surface is much cheaper than the same legends wrapped around the sides at different heights.

Beyond colour: breakaway supports

The AMS earns its keep on geometry as much as on appearance, and this is the application people underuse.

Load a second material as a support interface, one that doesn't bond strongly to the part material, and overhangs are supported by something that snaps away cleanly. Instead of the scarred, pitted surface that same-material supports leave behind, you get a smooth face.

This changes what's designable. Internal cavities, enclosed channels and deep undercuts that would be impossible to clean up by hand become straightforward. Parts that would have to be split into two pieces and glued can be printed whole.

If you've a design with an internal feature you assumed was unprintable, it's worth asking. It often isn't.

What you can and can't combine

Colours of the same material, no restrictions. Four PLAs, four PETGs, four ASAs. This is the common case and it always works.

Different materials, possible where the materials print at compatible temperatures and bond to each other. PLA with PLA-CF works well. PETG with a soluble support interface works well. Combining materials with very different print temperatures, or poor mutual adhesion, produces a part that delaminates at the boundary. We'll tell you if a combination won't hold.

TPU, not available in AMS jobs. TPU is flexible, and the AMS feed path involves tight bends and a buffer that soft filament buckles in rather than pushing through. TPU therefore prints from an external spool straight into the extruder, which rules it out of multi-material work. TPU parts are still available as single-material prints.

More than four filaments, not in one print. Four is the hardware ceiling. A part needing more can be split into sections printed separately, or you can accept a paint pass for the extras.

Where multi-colour pays

Not every part benefits. These are the cases where it clearly does:

Printed-in labelling. Legends, warnings, part numbers and indicators in a contrasting colour. These never wear off, unlike printed labels or engraved-and-filled text.

Colour-coded fixtures. In a workshop running several product lines, a fixture whose colour tells you which line it belongs to prevents mistakes. The colour is functional information.

Branded enclosures. Company colours in the part itself, with no paint line, no masking and no minimum order.

Legibility of geometry. On a complex model, an assembly cross-section, an architectural piece, a teaching aid, a contrasting colour makes the geometry readable in a way a single colour can't.

Two-durometer parts. A rigid body with a compliant grip, printed as one piece. (Note the TPU restriction above; this works with other flexible-adjacent combinations.)

Where it doesn't

Large single-colour production runs. Obviously, the AMS adds nothing but the surcharge isn't charged if you don't use it.

Parts that will be painted anyway. If the final finish is paint, print in one colour and paint it.

Purely cosmetic colour on an internal part. Nobody sees the inside of an enclosure.

Anything where the four-colour ceiling is a problem. If you need eight colours, this isn't the process.

Practical notes

Colour matching. Filament colours vary between manufacturers and between batches. If exact brand colours matter, tell us before we print rather than after. We can check what we've against a reference, but we can't match a Pantone exactly.

Bleed at transitions. Purging is very good but not perfect. On a sharp boundary between strongly contrasting colours, black to white is the worst case, there can be a very slight tint in the first fraction of a millimetre. Ordering the colours light-to-dark helps, because a trace of white in black is invisible while a trace of black in white isn't.

Layer alignment. Colour boundaries follow layer lines, so a horizontal boundary is crisp while a shallow-angled one steps slightly. Design colour transitions to run horizontally where crispness matters.

Getting a price

The estimator has a multi-material checkbox. Tick it and the price updates with the purge waste and time included, so there are no surprises. It disables itself automatically if you've selected the K1 Max, which has no AMS, or TPU, which can't be routed through it, with a note explaining why.

For a part with a complex colour layout, send the model and describe what goes where. We'll tell you roughly how many swaps it implies and, if the number is high, whether a small design change would bring it down. That conversation has saved customers a lot of money, and it takes about five minutes.