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If you print brackets, enclosures, or anything that sees load, wet filament is a mechanical problem as well as a cosmetic one. Water absorbed into the plastic turns to steam in the hot end. Prusa’s drying guide says high moisture content can cause low layer adhesion, blobs on the prints, and bubbling and smoke during extrusion. Layer adhesion is already the weak axis of an FDM part, and TDS numbers are measured on ideal specimens, so you don’t want to give up more Z-strength to steam voids.

There are three practical ways to dry a spool: a dedicated dryer box, a food dehydrator, or your printer’s heated bed. What matters is whether the method reaches the temperature your material needs, holds it accurately, and moves humid air out.

What temperature does your material need?

The numbers vary by manufacturer, so use the TDS or spool label for your specific brand. As a baseline, Prusa lists PLA/rPLA at 45 °C for 6 hours, PETG at 55 °C for 6 hours, and TPU at 60 °C for 4-6 hours. Bambu Lab is a bit hotter. One roundup of its settings shows Bambu PLA at 50 °C for 8 hours in a drying oven, while Prusa dries its PETG at 55 °C and Bambu uses 65 °C for PETG Basic.

Material Typical drying setpoint Time Source
PLA 45–50 °C 6–8 h Prusa / Bambu
PETG 55–65 °C 6–8 h Prusa / Bambu
TPU 95A 60–70 °C 4–8 h Prusa / Bambu
ABS, ASA 80 °C 8 h Bambu
PAHT-CF 80 °C 8–12 h Bambu

The last two rows come from Bambu’s forced-air oven settings: ABS and ASA at 80 °C for 8 hours, and PAHT-CF at 80 °C for 8-12 hours. That’s the real divider. PLA and PETG fit inside almost any cheap dryer. ABS, ASA, and nylon-family materials need a machine that runs 70 °C or more and can hold it.

Nylon, TPU, PC, and PVA are also in a different category for how often you dry. Bambu lists drying as required before use for these, even when new. PLA and PETG sit at the other end, where drying is recommended rather than required.

Dryer boxes: the default for a reason

A dryer box is a thermostat, heater, and fan in a spool-sized enclosure, usually with a hygrometer and a PTFE port so you can print straight out of it. That last feature matters more than it sounds. Bambu’s own guidance says typical indoor air runs 45–65% relative humidity, and that at around 55% RH freshly dried filament can start absorbing moisture again within 2–12 hours. Printing from the box keeps a long TPU or nylon job from re-wetting halfway through.

The main limit is the temperature ceiling. Most popular models stop at 70 °C. The SUNLU S2 single-spool dryer lists a 70 °C max, one spool, and a humidity readout, and one price tracker has it at $44.99. The four-spool SUNLU S4 is also capped at 70 °C. Its official store listed a sale price of $116.99 against a regular $139.99. SUNLU’s higher-end E2 is pitched at engineering filaments with up to 110 °C and a $300–$360 price range.

A 70 °C box covers PLA, PETG, TPU, and, slowly, ABS/ASA. For nylon and carbon-filled nylon it’s marginal. Forum users report success drying PET-CF and PAHT-CF in 70 °C dryers even though Bambu specifies 80 °C for 8-12 hours. They get there with longer runs, and results vary with room conditions. If nylon is your main material, budget for the higher-temperature unit or an oven.

One more caveat. The humidity number on the display is the air, not the plastic. As one forum poster put it, proper drying needs low RH held long enough for moisture to diffuse out of the plastic. A low reading after 30 minutes doesn’t mean the spool is done.

Food dehydrators: cheap airflow, uneven accuracy

A dehydrator is a heater and fan in a stack of trays. It moves a lot of air, which is the part cheap dryer boxes often skimp on, and it’s inexpensive. The catches are temperature range and calibration.

Range first. The Nesco Gardenmaster line, a common pick, is specified at 90°F to 160°F on the digital FD-1040, which is about 32–71 °C. That ceiling matches a typical 70 °C dryer box. The Nesco Gardenmaster FD-1040 was listed at $149.99 in one 2026 roundup, so it isn’t automatically cheaper than a dryer box. It does hold several spools, and you can remove trays to fit them.

Now calibration. Chitu Systems ran a one-hour comparison against its own dryer. With the dehydrator set to 50 °C, the chamber sat around 39 °C, and at a 70 °C setting it reached only about 51 °C. Chitu is a dryer vendor and tested one low-cost unit, and it said the result doesn’t prove every dehydrator is bad. Still, it’s a good reason to put a probe thermometer inside. Dehydrators typically sense temperature near the heater, not at the spool.

An older CNC Kitchen test shows both sides. In his dehydrator, drying curves for ASA, PLA, PETG, and CF nylon all flattened after about 12 hours, but the carbon-fiber nylon didn’t dry properly. He concluded his dehydrator wasn’t sufficient for some of his more demanding filaments. For PLA, PETG, and TPU it works. For nylon, you want an oven or a hot dryer.

Two practical notes: put spools on plastic spools only, and don’t use a dehydrator that also dries your jerky if you share it with the kitchen and that bothers you. Bambu also warns that some third-party spools may deform during drying, so check the spool material before you trust a given setpoint.

Heated bed: free, slow, and printer-dependent

The heated bed is the zero-cost option. Bambu documents a 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. Bambu’s wiki says to remove anything above or below the heatbed and take the filament out of the tool head, and it also notes that P1P, A1, and A1 mini are open printers and don’t support filament drying.

Bed setpoints are far higher than dryer setpoints because the spool sits in a loosely covered pocket, not a sealed hot-air chamber. Bambu’s published heatbed figures include 75–85 °C for 12 hours for PETG and 90–100 °C for 12 hours for PA and PA-CF. For PLA the heatbed setting is 60–70 °C, and you should turn the spool over every 6 hours so both sides dry. Bambu also cautions that heatbed drying of PPA-CF/GF and PPS may not be as effective as a convection oven.

The tradeoffs are real:

  • It ties up the printer. One forum poster put it as 16 hours at 100 °C with the machine unable to do anything else, and bought a dryer for that reason.
  • There’s no closed-loop control of the spool temperature. The bed temperature is not the spool temperature, and a cardboard box is not an insulated chamber.
  • The spool sits against a hot plate. Someone on the Bambu forum suggested lifting the spool off the bed so it doesn’t take the full bed temperature directly. Bambu’s flip-halfway instruction exists for the same reason.
  • Don’t leave it running unattended for long periods. That’s my own safety call, not a spec.

Side by side

Dryer box Food dehydrator Heated bed
Typical ceiling 70 °C (budget), 110 °C (SUNLU E2) about 71 °C (160°F) Printer bed limit, around 100 °C
Temperature accuracy Good, but reads air Needs a probe; one test read low No spool-level control
Airflow Fan, small vent Strong Passive
Print while drying Yes, often straight from the box Yes No
Nylon / CF-nylon Marginal at 70 °C, fine at 110 °C Poor Possible per Bambu, but slow
Cost About $45–$360 About $150 in one roundup $0

Which one for which part

For PLA or PETG brackets, jigs, and enclosures, any of the three works. Pick on convenience: a dryer box if you print weekly, a dehydrator if you want to batch several spools, the bed if you dry once a year. If you’re choosing PETG for load-bearing parts, the PETG brand comparison covers which spools have the better TDS numbers, and PLA vs PETG covers the base trade-offs.

For TPU, use a dryer box and print from it. Pick a gentle setpoint, because Bambu’s documentation says PLA, PVA, support filaments, and TPU shouldn’t be dried statically in its enclosed dryers, since their low softening temperatures let layers stick together. Rotating-spool drying avoids that. That is Bambu’s guidance for its own dryers, not a rule for every box, but it’s a sign to keep TPU temperatures conservative.

For ABS, ASA, PC, and nylon, which are the parts that usually see heat or real load, the 70 °C class of dryer is the weak link. Get a higher-temperature dryer or use an oven that you’ve verified with a thermometer. If you run an enclosed Bambu like the P1S, my P1S long-term review covers it, and the heatbed method is documented for it. The AMS 2 Pro combo post is the one to read if you’re considering drying built into the AMS. That unit tops out at 65 °C and isn’t compatible with ABS, ASA, PC, nylon, or PET-CF.

Don’t skip storage

Drying is temporary unless you seal the spool afterward. Bambu’s data sheets call for under 20% relative humidity, sealed with desiccant for printing and storage. Even at 20% RH, Bambu says filaments generally stay dry for only 2 to 7 days, depending on the material. A bagged spool with fresh desiccant and a cheap hygrometer will do more for your Z-axis strength than running a dryer longer.

A useful check: weigh the spool before and after. One forum poster reported that new 1 kg spools often lose 4 to 8 grams after the first drying. That’s anecdotal, but it’s a cheap sanity test that moisture actually came out.

Bottom line

If you only print PLA and PETG, a $45-class dryer box or a dehydrator with an external thermometer is plenty. If you print nylon, ASA, or carbon-filled engineering materials, buy for temperature ceiling first and capacity second. Use the heated bed as a backup when you need one spool dry this afternoon, and verify the temperature with a probe.

Sources