How to Dry Filament on Bambu Lab Printers: AMS 2 Pro, AMS HT and Heatbed Settings

Why prints get worse when the weather turns

Almost every common filament is hygroscopic: it pulls moisture out of the air around it. When that moisture reaches the hot end it turns to steam inside the melt, and the result shows up as stringing, bubbles, rough surfaces and weaker layers.

How quickly that happens is the part most people underestimate. Bambu Lab's own guidance puts typical indoor air at 45–65% relative humidity, and says that at around 55% RH, freshly dried filament can start absorbing moisture again within 2–12 hours. At 20% RH, the same spool stays dry for roughly 2–7 days.

Autumn and winter push indoor humidity the wrong way for months at a time. Windows stay shut, the heating cycles on and off, washing gets dried indoors, and damp outdoor air finds its way in. Meanwhile, spools that live on the AMS or a spool holder for weeks are exposed to all of it, around the clock.

Wet filament or bad settings? How to tell

Wet filament and bad settings produce overlapping symptoms, which is why people often spend an evening tuning retraction for a spool that just needed drying. These are the patterns that separate them:

The fastest test is to print the same small, string-heavy model from a freshly opened or freshly dried spool. If the problem disappears, it was moisture. If it doesn't, work through the settings instead: our PETG stringing guide covers the diagnostic order, and Bowden vs direct drive explains why retraction values copied from other printers so often cause trouble. Bambu Lab's own advice is simple: if you're not sure whether a spool is dry, dry it.

Drying temperatures and times by material

These are the drying settings published in the Bambu Lab Wiki. The first column is for a forced-air drying oven or dedicated filament dryer. The second is Bambu Lab's heatbed method on enclosed printers, covered in more detail below.

The heatbed figures are higher for a reason: the bed temperature isn't the temperature the filament actually sees. Heat has to travel up through the air under the cover, so the spool itself runs cooler than the plate beneath it.

Drying in the AMS 2 Pro and AMS HT

The AMS 2 Pro and AMS HT both dry filament in place, rotating the spools as they go so they dry evenly, and both report temperature and humidity on the unit, in Bambu Studio and in Bambu Handy. The difference that matters is the temperature ceiling.

Bambu Lab is direct about this: ABS, ASA, PC, PA and PVA need higher temperatures than the AMS 2 Pro can reach, so it recommends the AMS HT for fully drying them. The AMS 2 Pro will still take the edge off a slightly damp spool of those materials, but it won't do the job a proper drying cycle does.

The rules that catch people out

• No standalone drying. The unit has to be connected to the printer by its 6-pin bus cable to power on and enter drying mode, using the official power adapter.
• Not while it's feeding the print. An AMS that the current job is using, including one set up for auto-refill, can't dry at the same time. A unit the job isn't using can, though drying power may be reduced so the print gets priority.
• RFID only covers Bambu spools. Bambu Lab filament is matched to its drying settings automatically. Third-party spools need the temperature and time entering manually: use the dryer column above, capped at the unit's maximum.
• Lower PLA defaults are deliberate. If the PLA preset in your AMS looks cooler and longer than the oven figure, that's intentional: PLA sitting in the feed path softens at higher temperatures, so a gentler cycle is safer with filament loaded.
• Compatibility depends on printer and firmware. Some combinations, such as X1 and P1 series printers, need extra adapters or firmware updates before drying is supported, so check Bambu Lab's compatibility notes for your setup and keep firmware current.

Drying on the heatbed, no dryer needed

If you don't have a dryer or a drying-capable AMS, Bambu Lab documents a heatbed method for its enclosed printers:

• Place the spool flat on the build plate and cover it with a filament box or a clear PC box to hold the heat in.
• Set the bed to the heatbed temperature from the table above and close the door.
• Run for around 12 hours, turning the spool over every 6 hours so both sides dry.
• Move the spool straight into sealed storage, or onto the printer, once it's done.

It's slower and less even than a dedicated dryer, but it works, and it's often the difference between a failed nylon print and a good one when nothing else is to hand.

Keeping filament dry once it's dry

Drying is only half the job. Bambu Lab's guidance is to store most filaments below 20% RH for long-term dryness, which normal room air won't give you at any time of year.

• Seal it. An airtight box or vacuum bag with fresh desiccant is enough for most spools.
• Measure it. A cheap hygrometer in each storage box tells you when the desiccant has given up, rather than finding out from a failed print.
• Refresh the desiccant. Desiccant that has turned lumpy or pasty has stopped working and needs replacing or regenerating, including the packs inside the AMS.
• Don't park spools for weeks. A spool sitting on the AMS between jobs is exposed the whole time. Either return it to storage, or run a drying cycle before the next long print.
• Write down when it was dried. "Was this dried last week or last month?" is the question nobody can answer from memory.

A five-minute autumn checklist

1. Check the humidity reading on your AMS, or on a hygrometer next to the printer.
2. Replace or regenerate any desiccant that has gone lumpy.
3. Dry the spools you'll use this week, starting with the ones listed as required: TPU, PC, PA and PVA.
4. Note the date each spool was dried.
5. If a print still strings after a proper drying cycle, it's a settings problem: start with retraction.

Frequently asked questions

Sources: Bambu Lab Wiki: Filament drying recommendations · Bambu Lab: AMS 2 Pro