How to dry filament: temperatures, methods and storage, by the makers' rules

Why filament takes on water

Most FDM materials are hygroscopic: they pull water from the air. Prusa notes that some absorb far more than others, naming polyamide (nylon), polypropylene, PVA and BVOH as highly hygroscopic, and polyamide, PVA and TPU as the filaments most often in need of drying ^[1].

The damage happens in the hot end. Bambu Lab’s guide explains that absorbed moisture turns to steam in the nozzle, making the molten plastic expand and extrude erratically, which leaves bubbles, stringing, oozing, holes, rough surfaces and weaker parts, and that the effects grow with humidity and exposure time ^[2]. Prusa lists poor surface quality as the usual first sign, followed in worse cases by weak layer adhesion, blobs, bubbling and smoke at the nozzle ^[1]. The wet filament page covers diagnosis.

How hot, how long

Use the maker’s numbers for the spool in your hands. Recommendations for the same material differ between brands because formulations and assumed equipment differ. A few published values:

Sources: Prusa’s drying table and Bambu Lab’s drying appendix ^{[1, 2]}. Polymaker’s PolyMide CoPA nylon sheet gives 100 °C for 8 hours ^[4]. The drying chart lists every value in the database, and the drying planner groups spools that can share a run.

The temperature is a ceiling as well as a target. Prusa says not to exceed its values or the filament will soften and stick together, and to keep to the recommended times to avoid over-drying ^[1].

Methods the makers document

A filament dryer or drying AMS

A dedicated dryer is the most controlled option at home. Prusa’s advice is to check that the dryer’s maximum temperature matches the filament before buying one ^[1]. Bambu Lab’s AMS 2 Pro dries filaments that need up to 65 °C, while the AMS HT handles all of its filaments, though it says some high-temperature materials such as PVA may still not dry fully ^[2]. Bambu Lab also lists the AMS 2 Pro as unable to dry ABS and ASA at all, and says it may not fully dry TPU ^[2].

Two practical rules from Bambu Lab’s guide: when drying a high-temperature filament such as ABS, take the PLA out of the unit, and do not use the static (non-rotating) drying mode for PLA, PVA, its PLA/PETG support filament or TPU, because their windings can stick or deform ^[2].

The printer’s heated bed

Bambu Lab documents drying on the heated bed of its enclosed printers: unload the filament so it cannot soften in the extruder, lower the bed, set the spool on it under a cover (a printed PC or PA-CF lid, or the filament box), flip the spool halfway through, and let it cool before handling ^[2]. Its appendix lists bed temperatures and times per material, for example 60–70 °C for 12 hours for PLA Basic ^[2]. Bambu Lab says its open-frame printers cannot be used this way ^[2].

Safety: Bambu Lab advises gloves when flipping a hot spool ^[2].

Ovens

Here the makers disagree. Bambu Lab’s PLA data sheet calls for a blast (forced-air) drying oven with even temperature and says a microwave or kitchen oven is not compatible ^[3]. Prusa allows a conventional oven but warns that home ovens regulate temperature loosely, recommends an external thermometer, and notes that many cannot be set low enough for filament without damaging it ^[1]. For low-temperature materials like PLA, a dryer is the safer choice.

Food dehydrators

Prusa mentions adapted food dehydrators, with the trays removed to fit a spool, and warns that they usually reach only low temperatures ^[1].

The spool is part of the equation

Spools have temperature limits too. Prusa states that its current black Prusament spools withstand up to 90 °C, but that older spools with pressed-in plastic sides should not be heated above 45 °C unless a screw is added to hold the sides together ^[1]. Bambu Lab warns that some third-party spools may not be heat-resistant enough and could deform ^[2]. Check before a hot run, especially at nylon or PC temperatures.

Keeping it dry afterwards

Drying only helps if the filament stays dry. Prusa recommends a closed box or bag with desiccant, or vacuum bags with a desiccant inside, and suggests prioritising the most hygroscopic materials if space is limited ^[1]. Bambu Lab’s PLA data sheet sets printing and storage humidity below 20% RH, sealed with desiccant ^[3], and Polymaker asks for the same limit, below 20% RH, for PolyMide CoPA during storage and use ^[4]. Bambu Lab’s guide says to move dried, moisture-sensitive filaments straight into a sealed container or a desiccated AMS and use them soon ^[2].

For nylon and other highly hygroscopic materials, Prusa recommends either keeping them in a dry environment or drying them before every print ^[1]. Printing directly from a dry box removes the gap between drying and printing entirely.