How to Dry Filament: Temperatures by Material

A wet spool is the most commonly misdiagnosed fault in FDM printing, because every symptom it produces looks like a printer problem. Retraction tuning, nozzle swaps and bed relevelling all fail to fix it, and the machine gets blamed for a fault that lives in the material.

Drying is the fix, and it is a temperature-controlled process with a different correct temperature for every material. Getting the temperature wrong in one direction wastes hours; getting it wrong in the other direction fuses the spool to itself.

What a wet spool actually looks like

Bambu Lab’s filament documentation describes the mechanism directly: filament absorbs moisture from the air, and during printing that moisture rapidly vaporises inside the hot nozzle, causing the molten filament to expand and extrude erratically and form bubbles. The listed consequences are stringing, oozing, holes, rough surfaces and reduced strength, and the documentation notes these become more pronounced as ambient humidity rises or exposure time lengthens.

In practice the tells are:

• Popping, hissing or crackling from the nozzle during extrusion.
• Fine stringing that no retraction setting improves.
• A rough, matte or foamed surface on a filament that used to print glossy.
• Visible pits or holes in what should be a solid extrusion.
• Parts that snap between layers under loads they used to survive.

The last one matters most for functional parts. A wet spool does not just look worse, it prints weaker.

There is a faster test than printing something. MatterHackers’ guidance is to extrude a length of filament and watch it: bubbles, hissing, popping or cracking, or visible steam coming off the strand mean the spool is wet and needs drying. It takes thirty seconds at the machine and settles the question before any settings get touched.

How fast filament gets wet

Bambu Lab’s storage guidance puts numbers on the exposure that most people underestimate. Typical indoor relative humidity sits between 45% and 65% RH and rises further in humid weather. Most filaments only remain dry in an environment below 20% RH, and even there they stay dry for roughly two to seven days depending on the material. In a typical indoor environment around 55% RH, freshly dried filament absorbs enough moisture to affect print quality within two to twelve hours, depending on how hygroscopic the type is.

Some materials are far worse. Prusa’s documentation on polyamide notes that improper storage can lead it to absorb water weighing up to 10% of the filament weight. Bambu Lab adds that polyamide-based filaments left in open air for around three months absorb so much moisture that a conventional convection oven at 80–90 °C, which is within the spool’s heat-resistance limit, struggles to dry them at all.

The practical conclusion is that “I resealed the bag” is not storage, and a spool sitting on an open shelf for a week is already a candidate for drying regardless of how it looks.

Drying temperatures and times by material

The table below uses the forced-air convection oven column of Bambu Lab’s published drying recommendations, which is the closest match to how a standalone filament dryer behaves.

Material	Forced-air oven temperature	Time	Drying needed
PLA (basic, matte)	50 °C	8 h	Recommended
PLA silk	55 °C	8 h	Recommended
PLA carbon or glass filled	50–60 °C	8 h	Recommended
PLA wood filled	55–65 °C	8 h	Required
PETG, PETG-CF	60–65 °C	8 h	Recommended
ABS, ASA	75–85 °C	8 h	Recommended
TPU (85A, 90A, 95A HF)	70 °C	8 h	Required
PC (polycarbonate)	75–85 °C	8 h	Required
PVA	75–85 °C	8–12 h	Required
PA6-CF/GF, PAHT-CF/GF	75–85 °C	8–12 h	Required
PET-CF	80 °C	8–12 h	Required

Two things about this table are easy to misread.

First, the temperatures published for drying inside a printer’s heated chamber are much higher than these, because the heat is indirect and the spool never reaches the bed temperature. Bambu Lab lists 60–70 °C of bed temperature for PLA and 90–100 °C for ABS and ASA in that method. Applying a heated-bed figure to a dryer or an oven will destroy the spool. Match the number to the method.

Second, the correct temperature is bounded above by the material’s softening behaviour, not by how fast you want the job finished. Bambu Lab’s documentation notes that PLA, PVA, PLA/PETG support material and TPU should not be dried statically at all in its enclosed dryers, because their low softening temperatures let the filament layers stick together or deform. Filament that fuses to itself on the spool is filament that snaps or jams on the next print.

Choosing a drying method

A dedicated filament dryer. The simplest option. It holds a controlled temperature in a small enclosed volume, and most units let the filament feed out while drying, which solves storage and drying at once. Check the unit’s stated maximum against the table above before buying: PC, PVA and the PA-CF and PAHT-CF grades all want 75–85 °C, so a dryer whose ceiling sits below that cannot finish the job on the materials that most need it. Bambu Lab draws the same line inside its own product range, noting that the AMS 2 Pro suits filaments needing no more than 65 °C and may not fully dry anything above that.

A forced-air convection oven. Bambu Lab’s guidance recommends a forced-air convection oven specifically, notes the chamber should not be too small, and says the spool should sit away from the heating elements so the temperature distributes evenly and the spool does not deform from localised overheating. For a single spool it gives a minimum internal size of roughly 250 mm deep, 250 mm wide and 90 mm high, based on a reusable spool measuring 200 mm in outer diameter and 67 mm high.

Not a kitchen oven, and never a microwave. The same documentation is explicit: microwave heating is uneven and its temperature cannot be controlled, and kitchen ovens have very uneven heat distribution where areas near the heating elements become extremely hot and easily damage the spool or the filament. MatterHackers makes the same point from the other direction, warning that most convection and household ovens do not regulate their temperature well at the low end of their range and can easily warp a spool or soften the plastic enough to fuse the strands together. That is the specific failure: a domestic oven asked to hold 50 °C is being asked to work far below the range it was designed to control.

The printer’s own heated chamber. For enclosed machines this is a documented method rather than a hack. Bambu Lab describes lowering the bed, placing the spool on the build plate, covering it with a high-temperature printed cover or the filament’s own packaging box, and running the bed at the material’s listed chamber temperature. The Bambu Lab P1S is one of the enclosed models the procedure is written for, with the bed temperature and timing set manually; the documentation states that its open-frame siblings, including the P1P, A1 and A1 mini, cannot be used for this at all. Two cautions travel with the method: unload the filament from the toolhead first so it does not soften inside the extruder and clog it, and check that a third-party spool is heat-resistant enough not to deform.

Practical points that change the result

Flip the spool partway through. Bambu Lab recommends flipping the spool midway when drying on a heated bed, and every six hours for some materials, so the side facing the heat source changes. Wear gloves; the spool is hot.

Do not dry filament that is not on a spool. Bambu Lab’s instruction for spool-free refills is to install the filament onto a reusable spool before drying it, not to put the bare coil into the heat.

Cool before sealing. Bambu Lab’s procedure ends by setting the bed to 0 °C and waiting until the spool is no longer hot to the touch before removing it. Sealing a warm spool into a container traps the humid air that comes with it.

Polycarbonate does not like repeated cycles. The documentation notes PC filament can become brittle after repeated heating and cooling cycles from accumulated thermal stress, raising the risk of the filament snapping during a print even though part properties are unaffected. Keep PC sealed with desiccant so it needs drying rarely, rather than drying it habitually.

Keeping it dry afterwards

Drying is a repair. Storage is the thing that stops the repair being needed weekly.

After drying, filament needs a sealed container with effective desiccant, or a dry box it feeds directly out of. A hygrometer inside the container turns “probably fine” into a number, and the target from Bambu Lab’s guidance is below 20% RH.

One misconception is worth killing here, because it wastes weeks. A sealed box with desiccant does not dry a wet spool. MatterHackers states it plainly: you cannot effectively dry filament by storing it in an airtight container with desiccant. Desiccant holds a low humidity around filament that is already dry; pulling water back out of a saturated spool takes heat. Putting a wet spool into a dry box and waiting is not a drying cycle, it is just a slower version of leaving it out.

Silica gel desiccant is regenerable rather than disposable. Bambu Lab’s instructions are to spread the beads no more than 2 cm deep in a heat-safe ceramic, glass or foil container, dry them at 80–90 °C, and never exceed 100 °C because overheating damages the silica gel structure. Lightly damp beads take one to two hours and fully saturated beads two to three. Beads can typically be regenerated 5 to 15 times, and should be replaced when the colour change becomes slow or they start to crack. Plastic containers are explicitly prohibited for this, and a dedicated tray rather than food cookware is recommended.

Indicating beads make the schedule visible: the colour change tells you the desiccant is spent, which is the moment the sealed box quietly stopped working.

Confirming it worked

The honest check is the print, not the process. Run the same model or a short retraction test before and after, on unchanged settings, and look for whether the popping and the fine stringing are gone. A material that was drying-limited improves visibly; one that was not tells you the fault is elsewhere in the machine.

Weight is a weaker but useful signal. Moisture uptake shows up as mass, so weighing a spool before and after a drying cycle on a kitchen scale gives a rough sense of how much water came out, once the empty spool weight is accounted for. The site’s filament weight and length calculator handles the tare subtraction and converts net weight to remaining metres, and how density links spool weight to printable length explains the conversion behind it.

What drying will not fix

Drying is not a general-purpose repair. It does nothing for a partial nozzle clog, a first layer that will not stick, dimensional error from an uncalibrated extruder, layer shifts from a loose belt, or warping caused by ambient temperature. If a fault is geometric or mechanical rather than surface-quality related, moisture is the wrong suspect.

The materials most worth suspecting first are the hygroscopic ones: nylon, TPU, PVA and polycarbonate, all of which Bambu Lab marks as requiring both drying before use and desiccant protection during use. PLA and PETG sit at the other end, where drying is recommended rather than required, but neither is immune. For which material to reach for in the first place, PLA, PETG and ABS compared by temperature, warping and enclosure needs covers the trade-offs, and what to buy for a first filament purchase covers where storage habits should start.