How to dry filament, and how to tell it's wet

The signs of wet filament, drying temperatures and times by material, and how to keep spools dry once they are.

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Updated 2026-10-16

Short answer

Wet filament strings, bubbles and prints rough surfaces. Dry it at the temperature the maker gives for that material, usually for 4 to 8 hours in a filament dryer. PLA needs the least heat. TPU, PETG, ABS and ASA need more.

After drying, store the spool in a sealed box with desiccant. In normal room air, freshly dried filament can take up enough water to show in prints within hours.

Signs of wet filament

Most filament takes up water from the air. When it reaches the hot nozzle, that water turns to steam. Bambu Lab's wiki explains that this makes the molten plastic expand and come out unevenly, with bubbles. The result shows in the print.

A rough or uneven surface. Prusa calls poor surface quality the general first signal.
Stringing that doesn't go away when you change retraction or temperature.
Bubbles, blobs and small holes in the surface, and bubbling or what looks like smoke at the nozzle.
Weak layers that split apart more easily than they should.

A test you can see

If you aren't sure the spool is wet, print the same small test before and after drying. The filament swatch generator works well for this. It makes a flat card with the material and color name on it and a row of thin steps from 0.2 to 1.0 mm.

Print one swatch from the spool as it is, and write "before" in the color name field. Dry the spool, then print a second one marked "after". Compare the top surfaces and the thin steps. If drying helped, the second card is smoother, with fewer bubbles and hairs. If both look the same, moisture is probably not the problem, and the cause is more likely temperature or retraction.

Keep the cards. A swatch box holds them upright like a card index, one box per material, so you have a record of each spool.

Drying temperatures by material

Makers give different values, even for the same type of filament, so check the label or the maker's page first. These are the values from three makers, for a filament dryer or an oven:

PLA: Prusa 45 °C for 6 hours. Polymaker 55 °C for 6 hours for PolyLite PLA. Bambu Lab 50 °C for 8 hours in a forced-air oven.
PETG: Prusa 55 °C for 6 hours. Polymaker 65 °C for 6 hours for PolyLite PETG. Bambu Lab 60–65 °C for 8 hours.
ABS and ASA: Prusa 80 °C for 4 hours for ASA. Bambu Lab 75–85 °C for 8 hours for ABS and ASA.
TPU: Prusa 60 °C for 4–6 hours. Polymaker 70 °C for 8 hours for PolyFlex TPU95. Bambu Lab 70 °C for 8 hours.

Reading the numbers

Stay below the softening point of the plastic. Prusa warns that above the recommended temperature the filament softens and the windings stick together. That is why PLA has the lowest values. Prusa also warns against drying for much longer than the stated time.

Check the spool too. Prusa notes that its older black spools can come apart above 45 °C, and Bambu Lab warns that some third-party spools may not take the heat and can deform.

Not every material needs it as often. Prusa names TPU, nylon (polyamide) and PVA as the ones that most often need drying, and Bambu Lab marks drying as required for its TPU and only recommended for PLA and PETG. For more on each material, see choosing a filament.

Dryer, oven or printer bed

A filament dryer is a small heated box that holds one or more spools. You set the temperature and the time. Some can dry while you print: Bambu Lab's AMS 2 Pro does, for example. 3DJake's filament storage rangePartner link has filament dryers and dry boxes. Check that the dryer reaches the temperature of the hottest material you print. Bambu Lab notes that its AMS 2 Pro dries at up to 65 °C and may not fully dry some materials, such as TPU.

A kitchen oven is risky. Bambu Lab's wiki advises against kitchen and microwave ovens, because the heat is uneven and the area near the heating elements can get hot enough to damage the spool. Prusa notes that many home ovens can't hold a low temperature accurately and suggests checking with a separate thermometer. Bambu Lab recommends a forced-air oven with room around the spool.

A food dehydrator with the trays taken out is another option that Prusa mentions. Most only reach low temperatures, so check the maximum against your material before you rely on one.

Some enclosed printers can dry filament on the heated bed. Bambu Lab describes this for its enclosed printers: put the spool on the bed, cover it with the cardboard filament box or a printed cover, keep the doors shut and turn the spool over halfway through. Its bed values are not the same as its oven values: for PLA, 60–70 °C for 12 hours on the bed against 50 °C for 8 hours in an oven. Bambu Lab states that its open-frame printers can't be used for this.

Keeping it dry

Drying only helps until the filament takes the water back up. Bambu Lab gives typical indoor air as 45–65 % relative humidity. In about 55 % humidity, freshly dried filament can take up enough water to affect prints within 2 to 12 hours, depending on the material. Below 20 % humidity, it stays dry for roughly 2 to 7 days.

So store spools in a sealed box or bag with desiccant, and close it as soon as you finish printing. Prusa suggests a closed box with desiccant or a vacuum bag. A small hygrometer in the box shows whether the desiccant still works.

Silica gel is the usual desiccant. The 3DJake silica gelPartner link uses orange indicator beads that turn blue-green when they are full, and 3DJake states that it can be dried again at 70 °C. Bambu Lab gives 80–90 °C for drying its silica gel in an oven and warns not to go above 100 °C. Use the temperature given for the gel you have.

To keep loose beads in a box, print a silica gel box. It has slotted vents that are narrower than the beads, and a round version fits in the core of a spool. Its tips say to print it in PETG or ABS if you want to dry the beads inside it, because PLA softens above 55 °C.

Common mistakes

Drying PLA too hot. It softens and the windings stick together. Stay at the maker's value.
Trusting the oven dial. Home ovens can run hotter or swing more than the dial shows. Check with a thermometer, or use a dryer.
Drying and then leaving the spool out. In normal room air it can take up enough water to matter within hours. Seal it with desiccant.
Drying everything at one temperature. TPU and PETG need more heat than PLA, and PLA can't take theirs.
Blaming the slicer first. If stringing doesn't respond to retraction or temperature, dry the spool before you change more settings.
Saturated desiccant. Indicator beads that have changed color no longer protect the filament. Dry or replace them.

Frequently asked questions

How do I know if my filament is wet?

Stringing that won't go away, rough surfaces, bubbles or blobs, and bubbling at the nozzle. Print a filament swatch before and after drying to compare.

What temperature should I dry PLA at?

Low. Prusa gives 45 °C for 6 hours, Polymaker 55 °C and Bambu Lab 50 °C. Check the value for your spool, because PLA softens easily.

How long does it take to dry filament?

Usually 4 to 8 hours in a dryer or forced-air oven, depending on the material and the maker. Drying on a printer bed takes longer, about 12 hours in Bambu Lab's table.

Can I dry filament in a kitchen oven?

Bambu Lab advises against it, because the heat is uneven. If you do, check the real temperature with a separate thermometer and keep the spool away from the heating elements.

Does new filament need drying?

Not always. It depends on the material and how it was stored. If a new spool shows the signs of wet filament, dry it like any other.

Products mentioned

Filament StoragePartner link Filament dryers and dry boxes for keeping spools free of moisture.
3DJAKE Silica Gel Desiccant, 500 gPartner link Silica gel to keep stored filament dry between prints.