Is my filament wet? A symptom checklist with drying times

How to use this checklist

Pick the material and how the spool has been stored, then tick every symptom you see on settings that printed well before. The checklist adds up points and returns a likelihood of low, possible or likely. It also shows the maker’s drying temperature and time. If you weigh the spool before and after drying, it tells you how much water came out.

Nothing here replaces a test print. Treat the verdict as a guide to which cause to check first.

How can you tell if filament is wet?

Listen and look at the nozzle. Popping or crackling during extrusion, and steam or tiny bubbles in the plastic, are the clearest signs: water boils as the filament melts. Heavier stringing, a rough surface and weak layers point the same way, but each also has causes unrelated to moisture.

Bambu Lab’s drying guide describes the mechanism: moisture in the filament vaporizes in the hot nozzle, the melt expands and extrudes unevenly, and bubbles form. It lists stringing, oozing, holes, rough surfaces and lower strength as the results. Prusa’s knowledge base names a similar set: poor surface quality, heavy stringing, low layer adhesion, blobs, and bubbling and smoke during extrusion. Polymaker’s print tips for PolyMax PETG say popping or cracking noises during extrusion mean the filament needs drying.

Symptoms, their points and the other suspects

Symptom	Points	Also caused by
Popping or crackling at the nozzle	3	A partial clog can sputter, but audible pops usually mean water
Steam, bubbles or pits in the extruded plastic	3	Smoke rather than steam can mean a nozzle set far above the material’s range
Stringing worse than usual	1	Nozzle temperature too high or retraction set wrong, which Prusa names as the main causes
Rough, fuzzy or dull surface	1	Overheating, a worn nozzle, or printing too fast for the hotend
Weak or brittle parts, layers splitting	1	Nozzle temperature too low or too much part cooling
Filament snapping on the spool	1	Age, and the tight bend near the spool core
Inconsistent extrusion	1	A partial clog, extruder tension or a tangled spool

PETG strings more than PLA even when dry; Polymaker’s tips call it “known for being stringy”. Tick stringing only when a spool strings more than it used to on the same profile.

A PLA spool that breaks where it bends off the reel is often blamed on moisture, but old PLA can turn brittle for other reasons, and drying does not always restore it. The checklist gives it one point for that reason.

How is the moisture likelihood scored?

The score is symptom points plus storage points plus one point for materials that must be dried. Zero to two points reads low, three or four reads possible, five or more reads likely. With no symptom ticked the result is always low, because storage and material alone do not show a spool is wet.

The rule in full:

• Symptoms. Popping or crackling and steam or bubbles score 3 each, because they point at water directly. The five other symptoms score 1 each.
• Storage. A sealed bag, dry box or freshly dried spool scores 0. Open to room air for under a week scores 0, for a few weeks 1, for months 2.
• Material. Add 1 when the maker lists drying as required before use. Bambu Lab’s drying table marks it required for TPU, PC, PVA and carbon-fiber nylon. Polymaker’s PolyMide CoPA sheet says the nylon should always be stored and used below 20% relative humidity, so the checklist treats plain nylon the same way.

These weights are this tool’s own rule, set so that one strong sign on its own reads “possible” and a strong sign plus supporting evidence reads “likely”. They are not measured probabilities.

Worked example: a PETG spool that pops

A PETG spool has sat on the printer for three weeks. It crackles at the nozzle and strings more than it did when new.

1. Symptoms: popping 3 + stringing 1 = 4.
2. Storage: open for weeks, 1.
3. Material: Bambu Lab lists drying PETG as recommended, not required, so 0.
4. Total 5: likely.

The checklist then shows 65 °C (149 °F) for 8 h, from Bambu Lab’s PETG Basic data sheet.

Drying temperature and time by material

The calculator uses the first column. The rest show where Prusa’s and Polymaker’s published settings differ. All values are for a forced-air oven or dedicated dryer, not a printer’s heated bed.

Material	Setting used by the checklist	Prusa knowledge base	Polymaker
PLA	50 °C (122 °F), 8 h, Bambu Lab	45 °C, 6 h
PLA-CF	55 °C (131 °F), 8 h, Bambu Lab
PETG	65 °C (149 °F), 8 h, Bambu Lab	55 °C, 6 h	65 °C, 6 h (PolyLite PETG)
PETG-CF	65 °C (149 °F), 8 h, Bambu Lab
ABS	80 °C (176 °F), 8 h, Bambu Lab
ASA	80 °C (176 °F), 8 h, Bambu Lab	80 °C, 4 h
TPU 95A	70 °C (158 °F), 8 h, Bambu Lab	60 °C, 4 to 6 h
PC	80 °C (176 °F), 8 h, Bambu Lab	85 °C, 5 h (PC Blend)
Nylon PA6/66	100 °C (212 °F), 8 h, Polymaker		100 °C, 8 h (PolyMide CoPA)
Nylon PA6-CF	80 °C (176 °F), 8 to 12 h, Bambu Lab
PVA	80 °C (176 °F), 8 to 12 h, Bambu Lab

Bambu Lab values come from each product’s technical data sheet and fall inside the forced-air oven ranges of its drying guide. The heated-bed method in that guide uses higher bed temperatures, for 12 h.

Prusa warns that exceeding these temperatures softens the filament and makes the loops stick together. Bambu Lab’s data sheets advise against a microwave or kitchen oven because they heat unevenly.

The spool matters too: Bambu Lab’s guide notes that some third-party spools deform at drying temperatures, and its PLA data sheet rates Bambu’s own ABS spool to 70 °C.

How long should you dry PETG, and at what temperature?

Dry PETG at 65 °C (149 °F) for 6 to 8 hours. Bambu Lab’s PETG Basic data sheet gives 65 °C for 8 hours in a forced-air oven, and Polymaker’s PolyLite PETG sheet gives 65 °C for 6 hours. Prusa’s knowledge base lists a gentler 55 °C for 6 hours. Check your own spool’s label first.

Why the PETG numbers differ

The three makers test their own formulations, and each figure is a setting that works for their product rather than a physical constant. Treat Prusa’s 55 °C as the cautious end. If your spool’s label or data sheet gives a setting, use that. When it does not, 65 °C for 8 hours falls inside both Bambu Lab’s and Polymaker’s guidance.

Can you weigh filament to check if it is wet?

Yes, if your scale reads to 0.1 g. Weigh the spool, dry it, and weigh it again straight away. The loss is water. Compare it with the most water the material can hold: Bambu Lab’s sheet puts PETG at 0.45% at 25 °C and 55% humidity, so a fully soaked 1 kg spool loses about 4.5 g.

Most water each material takes up

Material	Water absorption	Most loss from 1 kg of filament
PLA	0.43%	4.3 g
PLA-CF	0.42%	4.2 g
PETG	0.45%	4.5 g
PETG-CF	0.30%	3.0 g
ABS	0.65%	6.5 g
ASA	0.45%	4.5 g
TPU 95A	1.08%	10.8 g
PC	0.25%	2.5 g
Nylon PA6/66	2.82%	28.2 g
Nylon PA6-CF	2.35%	23.5 g
PVA	6.25%	62.5 g

All figures are saturated water absorption at 25 °C and 55% relative humidity from the Bambu Lab data sheets, except nylon PA6/66, which is Polymaker’s equilibrium water absorption for PolyMide CoPA.

Worked example: weighing a PETG spool

A spool of PETG with 1,000 g of filament weighs 1,245.0 g before drying and 1,241.2 g after.

1. Loss: 1,245.0 − 1,241.2 = 3.8 g.
2. As a share of the filament: 3.8 / 1,000 = 0.38%.
3. Against the 0.45% maximum: 0.38 / 0.45 = 84%.

The spool was carrying most of the water PETG can hold, so the drying was worth doing. A loss near zero after a full cycle means moisture was not the problem, and the causes in the symptoms table come next.

Two limits apply. The spool itself can gain or lose a little moisture, and a scale that reads only to 1 g cannot resolve the 2.5 to 4.5 g swings of PC, PETG or PLA. The test is clearest with nylon, TPU and PVA, where the numbers are larger.

What if the symptoms stay after drying?

Then moisture was not the cause, or not the only one. Work through the “also caused by” column: lower the nozzle temperature, recheck retraction and look for a partial clog. Prusa’s stringing guide suggests trying a different spool on the same settings. If that spool prints clean, the old one is at fault; if not, suspect the settings.

Once a spool is dry, keep it that way. Bambu Lab’s guide says to store dried filament sealed with desiccant and use it soon. To see how much of the spool is left before starting a long print, the filament length to weight converter turns a spool’s weight into meters.