You can recognise wet filament by three symptoms at once: popping and hissing in the nozzle, a dull, rough surface and stringing that no retraction setting removes. All it takes is an open spool of PETG sitting for two weeks in a room at 45 % humidity, and you start blaming the profile, the printer and the extruder — while the problem sits in the material itself. If you are after prevention alone, we have a separate guide: how to store and dry filament.
This guide is about something else — recognition. You will learn to tell moisture symptoms apart from badly chosen temperature, check a spool with three quick tests and dry it using parameters matched to the material rather than guesswork. Because the most expensive mistake in 3D printing is not a ruined print, it is three hours spent calibrating a problem that cannot be calibrated away.
Drying filament — starting settings (table)
These are the values you start from. Always stay at least 10 °C below the softening point of the material — otherwise, instead of drying the spool, you will fuse the windings together.
| Material | Temperature and time | Comment |
|---|---|---|
| PLA | 45–55 °C · 4–6 h | Do not exceed 55 °C — above 60 °C the spool starts to deform |
| PLA+ / Tough PLA | 50–55 °C · 4–6 h | Impact modifiers do not change the drying regime |
| Silk PLA | 45–50 °C · 4–6 h | Higher temperature dulls the gloss — stay at the lower end |
| PETG | 60–70 °C · 4–6 h | The most commonly waterlogged material in the workshop |
| HT-PETG | 65–70 °C · 4–6 h | Handles the upper range without risk of fusing the windings |
| ABS | 70–80 °C · 2–4 h | Absorbs slowly but dries quickly |
| ASA | 70–80 °C · 2–4 h | Behaves like ABS |
| TPU 95A / 98A | 50–60 °C · 6–12 h | Highly hygroscopic, needs a long cycle |
| PA (nylon) | 70–90 °C · 12–16 h | Absorbs in hours, not days — dry before every print |
| PA-CF / fibre-filled composites | 80 °C · 8–12 h | Same parameters as the base material, time closer to the upper limit |
| Storage after drying | below 15–20 % RH | Dry box with silica gel or a vacuum bag with desiccant |
Drying temperatures are not the same as printing temperatures — you will find the latter in our printing temperature table, and it is worth having both sets at hand, because wet filament tempts you to „crank up the nozzle”, which only masks the symptom.
Why filament absorbs water and why that ruins prints
Most polymers used in 3D printing are hygroscopic — water molecules penetrate the polymer structure straight from the air. We are not talking about droplets on the surface, but about moisture bound throughout the whole cross-section of the strand. That is why wiping the spool with a cloth achieves nothing, and a spool that looks perfect can print terribly.
The failure mechanism is simple. The nozzle runs at 200–260 °C, far above the boiling point of water. Moisture trapped in the material evaporates violently in the melt zone and tears the polymer stream apart from the inside. Hence the characteristic popping: those are micro-explosions of steam. The result is unstable flow, bubbles in the extruded path and a surface that looks as if someone went over it with sandpaper.
The second part of the problem is chemical. Water at high temperature accelerates hydrolysis — it breaks polymer chains. A print made from wet material is simply weaker mechanically, even if it looks acceptable. The effect is most visible with PETG and nylon, where the declared tensile strength can fall noticeably below catalogue values. Some symptoms are easy to confuse with ordinary stringing — if you are unsure, start with our guide to stringing and check whether your case really looks different.
The symptoms you must not ignore
Moisture rarely produces a single symptom. Usually at least two appear at once, and that is the best diagnostic signal — a settings problem normally shows up on its own and repeatably.
Popping, hissing and ticking in the hotend
The most unambiguous symptom. A quiet „pop” every few seconds, a hiss of steam or a sound like frying. If you hear it with a material that used to print quietly, at the same settings — it is water. Watch out for one confusion: extruder clicking in an even rhythm usually means under-extrusion or a clogged nozzle, not moisture. Moisture sounds irregular.
A rough, matte surface instead of a smooth one
Walls lose their gloss, small craters and irregularities appear scattered randomly across the whole print. The key word is „randomly”. Defects caused by settings fall into regular patterns — bands, repeating layer levels, rhythmic waves. Moisture has no rhythm.
Strings and whiskers that resist retraction
You increase retraction, drop the temperature by 10 °C, enable combing — and the cobweb is still there. That is the sign it is not the profile. Water vapour expands inside the nozzle and pushes material out even when the extruder is idle, so no retraction can stop it.
Delamination and cracking of finished parts
The print comes out looking fine, but breaks under light load, and the layers separate cleanly, like sheets of paper. Steam bubbles create voids at the layer boundary, and that is exactly where the crack starts. On PETG and nylon this is sometimes the only visible symptom.
Holes in the top layer and flow spikes
The top surface refuses to close, despite a correct number of layers and enough infill. The culprit is variable flow — sometimes too little material, sometimes too much, because the stream pulses. You see the same on infill: paths lose continuity in random places.
Colour change, smoke and smell
Rarer but telling: wet material can print lighter and more matte, and with nylon and PETG it can produce a visible wisp of steam above the nozzle. The smell becomes sharper than usual. At that point the spool is badly waterlogged.
How long it takes for filament to get wet
This is the number that surprises beginners the most. In a typical room at around 45 % humidity, with a spool left unprotected, the rough time until print quality clearly degrades looks like this: PLA 2–4 weeks, PETG 1–2 weeks, ABS and ASA 2–4 weeks, TPU 3–5 days, and nylon — hours. Yes, hours. A PA spool taken out of its bag in the morning can print worse by the evening.
That is why the rule is simple and does not depend on the material: a spool you are not currently printing from goes back into a sealed container. Sealed in a vacuum bag with fresh desiccant, every one of the materials above lasts more than six months without re-drying. Unprotected, you are counting in days or weeks.
It is also worth remembering that workshop humidity is not constant. In autumn and winter, with a temperature difference between the shop and outside, it can jump well above 45 % — and then all the times above shorten accordingly. A cheap hygrometer will tell you more about the causes of failed prints than another flow calibration.
Three tests you can run in five minutes
The extrusion test
Heat the hotend to the normal printing temperature for that material, manually push out 10–15 cm of filament and watch the stream. Dry material comes down as an even, glossy strand, straight down. Wet material spits, curls to the side, forms bubbles and hisses. This is the fastest and most reliable test — it needs nothing but the printer.
The sound test
Quieten the room and listen to the nozzle for a minute during continuous extrusion. Irregular pops and hisses mean water. If you only hear the even hum of the fans and the quiet grind of the feeder, the material is fine.
The weight test
A method for the curious: weigh the spool before and after drying. A difference of several to a dozen or so grams per kilogram of material confirms that water really did evaporate. This test will not diagnose the problem up front, but it verifies beautifully whether your dryer works at all.
Drying step by step
First, set the temperature from the table above and do not improvise upwards. Second, do not shorten the time — water leaves the inside of the strand slowly and half an hour changes nothing. Third, if you can, dry the spool in a device with forced air circulation; a heater without a fan only dries the outer windings.
Fourth — and this is the step everyone skips — after drying, the spool has to go into a dry environment immediately. Pulling out a warm spool and leaving it on the bench overnight can undo half the effect, because cooling material absorbs moisture more eagerly than cold material. A dry box, a vacuum bag with desiccant or a dryer running in maintenance mode during the print: pick one, but do it right away.
Fifth, check the result. Repeat the extrusion test. If the stream still spits, extend the cycle by another 2–4 hours instead of raising the temperature. Badly waterlogged material, nylon in particular, can need the full 16 hours.
Settings for popular setups
| Drying method | Settings | Notes |
|---|---|---|
| Dedicated filament dryer | Temperature from the table, full time | The safest option; many models let you print straight from the dryer |
| Fan oven | Lower end of the table range, door ajar | Ovens can overshoot the setpoint by 20–30 °C — check with a separate thermometer |
| Heated bed with a cover | Lower end of the range, 6–8 h | An emergency improvisation; uneven heating, risk of deforming the spool from below |
| Enclosed printer chamber | High-temperature materials only | Not suitable for PLA or TPU; no humidity control inside |
| Dry box with silica gel (storage) | Target below 15–20 % RH | Does not dry the material, only maintains its state; regenerate the desiccant when it changes colour |
| Vacuum bag with desiccant | Fresh desiccant every time you seal it | Over 6 months of storage without re-drying |
The most common mistakes
Drying at too high a temperature. PLA above 60 °C starts to soften and the windings fuse into a block no extruder will unwind — stay at 45–55 °C.
Cutting the cycle down to an hour. Water bound in the cross-section of the strand needs several hours to reach the surface; a short cycle only dries the outer windings and the symptoms come back halfway through the print.
Leaving the dried spool on the bench. Material absorbs most aggressively right after drying, so every hour in open air costs more than it did before the cycle — pack it immediately.
Adjusting print temperature instead of drying. Raising the nozzle by 10 °C sometimes improves wall appearance briefly, but it accelerates hydrolysis and makes the finished part weaker.
Confusing moisture with a clogged nozzle. Regular, rhythmic extruder clicking usually means a restriction in the material path; moisture sounds irregular and comes with a matte surface.
Trusting how the spool looks. Filament does not change colour or turn sticky from moisture — a factory-sealed spool stored without desiccant for a year can be wet too.
One dry box for the whole workshop. A container opened a dozen times a day will not hold low humidity; smaller, less frequently opened boxes with their own indicator work better.
Frequently asked questions
Does PLA need drying too?
Yes, although less often than other materials. PLA absorbs more slowly — in typical conditions clear symptoms appear after 2–4 weeks without protection. Drying at 45–55 °C for 4–6 hours is entirely enough.
How long does drying filament take?
From 2 hours for ABS and ASA up to 16 hours for badly waterlogged nylon. For the most popular materials, PLA and PETG, a realistic cycle is 4–6 hours. Cutting that short only gives the appearance of a result.
Can you dry filament in an oven?
You can, but carefully. Pick the lower end of the temperature range from the table, switch on the fan, leave the door ajar and verify the real temperature with a separate thermometer — domestic ovens often overshoot the setpoint by 20–30 °C, and that is enough to destroy a PLA spool.
Does drying fully restore the filament?
Print appearance and flow stability come back practically every time. Mechanical strength — not entirely, because hydrolysis of the polymer chains is irreversible. For load-bearing parts, use material that has not been sitting open for months.
How long does dry filament last outside a dry box?
It depends on the material and ambient humidity. At around 45 % RH it is weeks for PLA, ABS and ASA, days for TPU and hours for nylon. Sealed in a vacuum bag with desiccant, each of them lasts over six months.
Summary
Moisture is one of the few causes of print defects that cannot be fixed with settings — and that is exactly why it costs so much time. Remember the sequence: irregular popping plus a matte surface plus stringing that resists retraction means water, not the profile. Run the extrusion test, dry the spool using the parameters from the table and pack it away immediately after the cycle.
Technical materials are the least forgiving — nylon, carbon-fibre composites and elastomers demand storage discipline from day one. If you are just starting out with them, it is worth reaching for material packed at the factory with desiccant, for example Porima PA, and you will find the rest of our engineering range in the technical filaments category.