AMS multicolor printing cost: how much goes to purge waste

On a single-nozzle printer, the nozzle holds one color at a time. What makes a multicolor print expensive is not the number of colors, but how many times the machine has to switch from one to another.

Why every color change uses filament

On Bambu Lab's AMS and AMS Lite, Creality's CFS, Anycubic's ACE Pro and Prusa's MMU3, a change follows the same routine: the old filament is pulled back, the new one is loaded, and the extruder pushes out what is left of the previous color until only the new color comes out. That is the purge, or flush. On Bambu Lab printers it leaves through a chute and becomes the little blob of plastic many people call "poop". Then, by default, the nozzle prints a bit on the prime tower, a sacrificial structure that stabilizes the flow before returning to the model.

According to Bambu Lab's guide to reducing waste during filament change (checked November 2026), dark colors need more purge to switch to a light color, and the reverse needs less. And on each layer, the machine makes one change fewer than the number of colors on that layer, because the last color of one layer is the first of the next. So what drives waste is how many layers contain more than one color, not the size of the part.

Each change also takes time: in Bambu Studio's stock profiles, unloading and loading alone add up to 57 seconds on the X1 Carbon and the P1S, before the purge itself. The slicer's total time already includes it.

Where to see the purge in Bambu Studio and OrcaSlicer

After slicing, open the preview and switch the view to Filament. You get one row per filament, with these columns:

• Model: what stays in the part. Support shows up when the part has supports.
• Flushed: the purge that goes out through the chute.
• Tower: what went into the prime tower.
• Total: everything added up, which is what the print takes from each spool.

Below the table you see Filament change times, the number of changes, and Cost. OrcaSlicer shows the same columns. The rule for not counting anything twice:

• For cost, use Total. It already adds part, support, purge and tower.
• Color-change waste is Flushed + Tower. Use it to compare setups, not to add again on top of Total.
• Do not put a waste percentage on top of Total to cover the purge. A percentage only makes sense for losses the slicer cannot see, like a part you throw away because of a defect.

The math, with Bambu Lab's wiki numbers

Bambu Lab's example is a four-color cube that weighs 11 g and, at 0.2 mm layers, makes 153 changes with 83 g of waste. With PLA at $20 per kg ($0.02 per gram):

1. The part alone: 11 g × $0.02 = $0.22.
2. With purge and tower: (11 + 83) g = 94 g × $0.02 = $1.88. The waste alone costs $1.66, 7.5 times the material in the part.
3. Per change: 83 g ÷ 153 = about 0.54 g, purge and tower together.
4. Nine cubes on the same plate make the same 153 changes and the same 83 g of waste. Material goes to (99 + 83) g = 182 g × $0.02 = $3.64, or $0.40 per cube.

Then there is time: at 57 seconds per change just to unload and load, 153 changes add almost two and a half hours of machine time, before the purge itself. The guide to 3D printer cost per hour shows how to turn those hours into dollars.

How waste grows with the number of changes

A math example for a 20 g name sign ($0.40 of material) in two colors. With both colors on the same layer, each layer makes one change, so the number of changes follows the height over which the two colors share layers.

Assumptions: PLA at $20/kg, 0.2 mm layers, one change per layer and 0.54 g of purge and tower per change, the average of the Bambu Lab wiki cube. On your own project, the number that counts is the slicer's Flushed + Tower, which changes with the colors and the purge options.

How to spend less on color changes

1. Design for fewer layers with two colors. Raised letters sitting on top of the base change color only once, because the layers above the base hold only the letter color. Inlaid letters change on every layer that has both colors.
2. Try another orientation. In the wiki, laying a tall part down cut almost 80% of the changes and the waste: 11 hours and almost 180 g less on a part of about 35 g. But a part with colors in horizontal bands, laid down, wasted 22 times more. Slice both positions.
3. Use thicker layers when the finish allows. On the cube, going from 0.2 to 0.28 mm cut the changes from 153 to 111 and the waste from 83 g to 61 g: from $1.66 to $1.22.
4. Adjust the multiplier. In Bambu Studio, the Flushing volumes button opens the purge table for each color pair, with a Multiplier field. The default is 1.00, and 0.90 purges 10% less on every change. Bambu Lab suggests trying 0.8 or 0.9 with a test print, because too little purge leaves discolored layers.
5. Purge into the part. Under Others › Flush options, Flush into objects' infill spends the purge on the hidden infill. It is off by default and can show through with light colors, transparent filament or parts with few walls. Flush into objects' support is already on. Both need the prime tower enabled.
6. Use a sacrificial object. Flush into this object, set per object, purges into a part whose color does not matter, such as a functional part or one that will be painted. In the wiki, a cube that would purge about 70 g dropped to less than 1 g this way.
7. Group copies only if the colors line up on the same layers. Parts sharing the same colors, on one plate, went from 171 g to 133 g of waste. But three traffic cones with stripes at different heights went from 22 g printed separately to 72 g together.
8. Flip the part so the changes sit low. The tower has to rise to the last layer with a change: flipping the same part upside down cut the tower from 14.76 g to 9.05 g.

To see what a change is worth on your own print, slice the same plate twice, for example with the default purge and with flushing into infill or a 0.9 multiplier, and write down Flushed + Tower for each. Enter both numbers in the box below.

How to put color changes into the price

• Material: each filament's Total times the price of its spool. The guide to cost per gram of filament shows that math.
• Time: the slicer's total time, which already includes the changes and drives electricity and wear.
• Extra waste: zero for anything the slicer already counted.

In the MakerPrice 3D calculator, import the sliced 3MF (in Bambu Studio, Export plate sliced file) or the G-code: the weight of each color and the time fill in by themselves, purge included, and the waste field is set to zero so nothing is counted twice. What Bambu Studio's own cost leaves out is covered in Bambu Studio cost estimate vs real cost. Two-color keychains are the classic case where the purge outweighs the part; see the guide to keychain pricing.

Frequently asked questions

Can I drop the purge multiplier to 0.5?

You can test it, but the risk of discoloration grows exactly on dark-to-light changes, the ones that purge the most. A safer path is to lower only the pairs of similar colors, or light-to-dark pairs, in the table and keep the dark-to-light ones. Check on a test part before using it on an order.

Can I turn off the prime tower?

Yes, under Others › Prime tower. Without the tower, though, flushing into infill, support and objects stops working, and the purge still goes out through the chute. The tower also stabilizes flow at the start of each color, so turning it off can hurt the finish.

Why does black to white use more purge than white to black?

Because a little dark color shows a lot in a light color, while a little light color disappears in a dark one. Bambu Studio calculates the purge for each pair from the colors, and in its code transparent filament is treated as white. In the automatic order for each layer, it already picks the sequence with the least purge.

Does a dual-nozzle printer get rid of the purge?

It reduces it, but not to zero. Switching between nozzles skips almost all of the purge; when the part has more colors than nozzles, changes within the same nozzle still purge. The Flushed column shows how much is left.

Does printing a single color with the AMS waste filament too?

If the plate uses only one filament, there are no changes during the print and the slicer shows zero under Filament change times. All that is left is the prime line at the start, which every print has.