The Bambu AMS, explained
The AMS (Automatic Material System) is the four-spool box that makes Bambu printers feel effortless — it swaps colours for you, switches to a fresh spool when one runs out, and keeps filament tidy. It's genuinely great. But almost every new owner expects it to do one thing it can't.
Four spools, swapped automatically — over a desiccant tray that slows moisture, not removes it.
The short answer
What the AMS actually does
It holds up to four spools and feeds whichever the print needs, switching between them automatically. That buys you two things: multi-colour and multi-materialprints from a single nozzle, and hands-off long prints that continue onto a fresh spool when one runs dry. With Bambu's own filament it reads an RFID tag and loads the right settings for you. A desiccant compartment and a humidity card help keep the air inside dry.
The myth: it's not a dryer
The desiccant slows how quickly filament absorbs moisture — it does not remove moisture that's already in the plastic. So if a spool has been sitting open and now prints rough, bubbly, or stringy, parking it in the AMS won't fix it. Pull it out, run it through a proper drying cycle, then keep it in the AMS to stay dry. Refresh the desiccant when the humidity card changes colour.
What to run in it — and what to keep out
The AMS is built for firm filaments: PLA, PETG, ABS, ASA, and support materials all feed happily. What to keep out:
- TPU and flexibles — they buckle in the feed path and jam. Run them from an external spool holder instead.
- Cardboard-core or oversized spools — cardboard sheds dust into the mechanism, and very wide spools may not fit. Stick to standard plastic 1 kg spools.
- Abrasive filaments (carbon-fibre, glow-in-the-dark) feed fine but wear the path and nozzle over time — use them knowingly.
Tip
Multi-colour, and the waste that comes with it
Every colour change purges the old filament out of the nozzle so colours stay clean — that's the little pile of "poop" next to your print. It's normal, but it adds up: more colours and more swaps mean more wasted filament and longer prints. Keep colour counts reasonable, and remember the cost calculatorcan account for that purge waste when you're pricing a print.
AMS quick rules
- It's not a dryer — dry wet spools separately, then store them in it.
- Keep TPU and flexibles out; feed them from an external spool.
- Standard plastic 1 kg spools only — skip cardboard cores.
- Refresh the desiccant when the humidity card changes colour.
- Fewer colours = less purge waste and shorter prints.
Common questions
Does the Bambu AMS dry filament?
No — this is the single biggest misconception. The AMS has a desiccant compartment that slows how fast filament picks up moisture from the air, but it cannot pull moisture back out of a spool that's already wet. If a spool prints rough, bubbly, or stringy, take it out and dry it properly in a filament dryer, then keep it in the AMS to stay dry.
Can you use TPU in the AMS?
It's not recommended. Flexible filaments like TPU buckle and jam in the AMS feed path, which is built for firm materials. Run TPU and other flexibles from an external spool holder feeding straight into the printer instead. The AMS is happiest with PLA, PETG, ABS, ASA, and support materials.
Do I have to keep filament in the AMS?
No. The AMS is convenient and slows moisture uptake, but a spool sealed in a bag or box with fresh desiccant stores just as well — often better. Keep the spools you're actively using in the AMS, and seal the rest away. Don't treat the AMS as long-term storage for a dozen open spools.
How does multi-colour printing waste filament?
Every time the AMS swaps colours, it purges the old colour out of the nozzle so it doesn't contaminate the new one — the little 'poop' pile beside your print. More colours and more swaps mean more waste and more time. Keep colour counts sensible, and lean on models designed to minimise swaps.