3D printing process guide

How to dry 3D printing filaments and prevent moisture from forming

Wet filament shows up as popping, stringing, and weak layer bonds long before a print fails outright. This guide covers drying temperatures and times per material, how to store spools so moisture never comes back, and how we handle filament on the production floor at GreatLight.

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PLA, PETG, TPU, PA, PC40–80 °C drying rangeDesiccant + sealed storage

Wired 3D printing and how to dry 3D printing filaments before a print

On this page

1
Key takeaways
2
Why moisture ruins filament and what it looks like on the part
3
How fast each filament absorbs water, and which prints are at risk
4
Filament dryers, ovens, and vacuum bags: pick the right tool
5
Stopping moisture from forming again
6
How we handle filament and prototypes at GreatLight
7
Step by step: how to dry 3D printing filaments
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Drying temperature and time by filament

Quick answers

Key takeaways

Drying beats troubleshootingMost stringing, popping, and brittle parts trace back to absorbed water, not slicer settings.

Temperature is material-specificPLA dries near 45 °C; PA and PC need 70–80 °C. Too hot warps or fuses the spool.

Time depends on mass, not spool countA 1 kg spool needs 4–6 hours; a 250 g spool about half that.

Sealed storage is the real fixDry filament reabsorbs moisture within days in 60% RH shop air.

Weigh before and afterA 2–5 g drop on a 1 kg spool confirms the cycle worked.

Why it matters

Why moisture ruins filament and what it looks like on the part

Most 3D printing filaments are hygroscopic, meaning they pull water out of the air and hold it inside the polymer. Nylon is the worst offender, followed by PC, TPU, PETG, and ABS; PLA absorbs slowly but still does it. A spool left on an open shelf for two weeks can hold enough water that every extrusion becomes a small steam event.

The water flashes to steam inside the hot end at 200–300 °C. That expansion pushes molten plastic out unevenly, which is why wet filament pops, hisses, and extrudes a bead with a rough, matte skin instead of a smooth one. Layer adhesion drops because the steam leaves micro-voids at the bond line.

You can often hear it before you see it. Stand near the nozzle during a first layer and listen for a faint crackle. On the part itself, look for small pits, a cloudy surface on what should be glossy filament, and stringing that gets worse toward the end of a long print.

None of these symptoms is unique to moisture, so confirm before you run a drying cycle. Check that the nozzle is clean, the first layer is properly squished, and the temperature is right for the material. If settings are sane and the symptoms persist, weigh the spool and start drying.

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Popping or crackling at the nozzleSteam escaping the melt zone; the most direct sign of wet filament.
2
Stringing and oozing that settings cannot fixRetraction tuning helps, but wet filament keeps oozing regardless.
3
Weak, delaminating layersMicro-voids at the bond line cut tensile strength.
4
Cloudy or pitted surfaceWater vapor roughens the extruded bead.

Material behavior

How fast each filament absorbs water, and which prints are at risk

Absorption rate tracks polymer chemistry. Nylon (PA, PA-CF) can take on 2–4% of its weight in water within a day in humid air, and it prints badly at anything over about 0.2%. PC and TPU sit in the middle. PETG and ABS are slower but still measurable over weeks. PLA is the most forgiving, which is why beginners often blame the slicer when the real problem is a two-year-old spool.

Humidity, not time alone, drives the process. At 20% relative humidity a spool might sit for months without trouble. In a shop at 60–70% RH, especially during summer, a single overnight exposure is enough to affect a nylon part. Coastal locations and unventilated rooms are the worst cases.

Print geometry matters too. Long prints, tall thin walls, and parts under load in service all amplify the effect of weak layer bonding. A decorative desk toy may look fine with damp PLA. A structural bracket printed in wet PA-CF will crack at the layer lines, sometimes days after the print finishes.

Filament that has been dried and then left in a dry box behaves like new stock for weeks. That is the whole point of a drying routine: it is not a rescue operation, it is a storage discipline.

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High riskNylon, PA-CF, PC, TPU, and any filled or composite filament
2
Medium riskPETG, ABS, ASA, and most copolyester blends
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Lower riskPLA and PLA+ in normal shop humidity
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Sensitive partsLong prints, thin walls, and load-bearing functional parts

Method

Filament dryers, ovens, and vacuum bags: pick the right tool

A dedicated filament dryer is the easiest option for most shops. These units hold one or two spools at a controlled 35–80 °C and circulate air, so you set temperature and time and walk away. Look for a model that states a temperature range rather than fixed presets, because nylon and PC need 70–80 °C, which many entry units cannot reach.

A convection oven works if it holds low temperatures accurately. Household ovens typically bottom out around 70–100 °C and swing widely, so they are risky for PLA and PETG. Use an oven thermometer to verify the actual chamber temperature, not the dial. Never use a microwave; it heats unevenly and can melt the spool.

Food dehydrators are a popular budget route. They hold 40–70 °C well and move plenty of air, and a modified tray can fit two spools. The limitation is the top end: they rarely reach the 80 °C that PC and some nylons want.

Vacuum bags with desiccant are not a drying method on their own. They are excellent storage. If a spool is already wet, a bag will not pull water out of the polymer at any useful rate. Dry first, then seal.

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Filament dryerBest control; choose one rated to at least 80 °C
2
Convection ovenVerify with a separate thermometer; avoid wide-swing ovens
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Food dehydratorGood for PLA, PETG, TPU; limited top temperature
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Vacuum bag + desiccantStorage only, after drying

Prevention

Stopping moisture from forming again

Drying is a cycle, not a one-time fix. The same polymer that gave up its water in the dryer will start taking it back the moment it sees humid air. In a shop at 60% RH and 25 °C, a nylon spool can pick up noticeable moisture within 24 hours of leaving a dry box.

The practical answer is to keep every active spool in a sealed container with desiccant and to feed filament to the printer from inside that container. Many dry boxes have a PTFE tube port for exactly this. You get a closed path from box to hot end, and the spool never touches shop air.

For longer storage, vacuum bags with a desiccant packet and a heat seal or zip closure work well. Label each bag with the material, the dry date, and the weight so you know what you are reaching for. Rotate stock oldest first.

Track the room, not just the spools. A cheap hygrometer next to the printer tells you whether the shop is at 30% or 70% RH, and that number decides how often you recharge desiccant. If you print nylon regularly, a small dehumidifier for the printer enclosure area pays for itself.

Finally, keep a dry-box discipline for the printer itself. Filament left on an open spool holder overnight is the single most common way a freshly dried spool goes bad before the next job.

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Sealed dry box with PTFE feedSpool stays enclosed while printing; no exposure between jobs
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Vacuum bags for sparesLabel material, dry date, and weight
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Hygrometer at the printerRead RH directly instead of guessing
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Enclosure dehumidifierUseful when printing nylon or PC through a humid season

At the shop

How we handle filament and prototypes at GreatLight

GreatLight runs 3D printing alongside CNC machining in Dongguan, with a second plant in Singapore. For prototypes that need to match a machined production part, the printed version is often a fit and form check rather than a load-bearing component, so material choice and dryness still affect whether the check is meaningful.

We dry filament before any job that uses nylon, PC, or TPU, and we store active spools in sealed boxes with desiccant. Prints that will be compared against machined parts are checked for dimensional consistency; a wet spool produces a rough surface and slightly inconsistent extrusion, which makes that comparison harder.

When a project moves from printed prototype to production, the same geometry can be cut from aluminium 6061, 7075, stainless 17-4PH, or a plastic such as POM or PEEK on our CNC machines. Tolerances hold at ±0.005 mm and surface finish can reach Ra 0.2–0.8 μm when the drawing calls for it.

Uploads are handled confidentially, and an NDA is available on request. If you are deciding between printed prototypes and machined parts, send the drawing and we will give a straight answer on which process fits the quantity, material, and tolerance.

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Drying before nylon, PC, and TPU jobsTemperature per material, verified with a scale
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Sealed storage on the floorActive spools stay in dry boxes with desiccant
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Prototype to productionPrinted check parts, then CNC in metal or engineering plastic
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Confidential handlingNDA available on request

Procedure

Step by step: how to dry 3D printing filaments

Work through these in order. Total time is usually 4–8 hours for a 1 kg spool plus cooling and storage.

1
Identify the polymer before you set a temperatureCheck the spool label or the supplier data sheet. PLA 40–50 °C, PETG 60–65 °C, TPU 50–60 °C, ABS/ASA 65–70 °C, nylon 70–80 °C, PC 75–80 °C, PVA 45–50 °C. Never dry above the material's glass transition temperature; PLA softens near 60 °C and a fused spool is scrap.
2
Weigh the spool and record the numberA kitchen scale reading to 1 g is enough. Write it on a tag. You will weigh again at the end, and a 2–5 g loss on a 1 kg spool is normal confirmation that water left the filament.
3
Load the dryer and leave the spool free to rotateDo not stack spools so air cannot reach the filament surfaces. Set the spool on the roller, close the lid, and set the temperature from step 1. If the dryer has a vent, crack it slightly during the first hour to let humid air escape.
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Run the cycle for the right durationTypical times: 250 g spool 2–3 hours, 500 g spool 3–4 hours, 1 kg spool 4–6 hours. Nylon and PC sit at the long end, PLA and PETG at the short end. Filament that has been wet for months may need a repeat cycle.
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Cool the spool before printingTurn the dryer off and let the spool sit inside for 20–30 minutes. Moving a hot spool straight into cool shop air can cause condensation on the filament surface, which defeats the whole cycle.
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Move the spool directly into a sealed containerUse a gasketed dry box with 20–50 g of fresh silica gel per spool, or a vacuum bag with desiccant. Do not leave the spool on the printer's open holder between sessions unless the holder sits inside a sealed box.
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Recharge or replace desiccant on a scheduleSilica gel saturates. Orange-indicator beads turn green, or you can dry the gel at 100–120 °C for 2 hours and reuse it. In a humid shop, check monthly.
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Verify with a test print if the part is criticalPrint a small layer-adhesion test or a 20 mm cube and check for popping and surface cloudiness. If symptoms persist, run one more drying cycle and confirm the dryer's actual temperature with a thermometer.

Reference

Drying temperature and time by filament

Starting points only. Confirm against your supplier data sheet, and stay below the material's glass transition temperature.

Filament	Drying temp	Typical time (1 kg)	Storage RH target
PLA / PLA+	40–50 °C	3–4 h	Under 20% RH
PETG	60–65 °C	4–5 h	Under 20% RH
TPU / TPE	50–60 °C	4–5 h	Under 20% RH
ABS / ASA	65–70 °C	4–6 h	Under 20% RH
Nylon / PA-CF	70–80 °C	5–6 h	Under 15% RH
PC / PC blend	75–80 °C	5–6 h	Under 15% RH
PVA / BVOH	45–50 °C	3–4 h	Under 15% RH

FAQs

Frequently asked questions

Can I dry filament in a regular kitchen oven?

Only if the oven holds low temperatures accurately. Most home ovens bottom out near 70–100 °C and swing by 15 °C or more, which will soften PLA and can fuse a spool.

If you use one, put a separate oven thermometer on the rack and stay 10 °C below the material limit. A dedicated dryer or a food dehydrator is safer for PLA and PETG.

How often should I dry filament I use every week?

If the spool lives in a sealed dry box between jobs, you may only need to dry it once when it arrives. If it sits on an open holder in a humid shop, dry it before each long or critical print.

Weighing is the cheapest check. A spool that has gained 2–3 g since its last dry date has taken on water.

Does drying filament damage it?

Not at correct temperatures. Damage comes from overheating: PLA above roughly 60 °C, PETG above 70 °C, and nylon above 90 °C can soften, warp, or fuse the spool.

Repeated short cycles at the right temperature are safe. Very long cycles at high temperature can make some filaments brittle, so follow the material range rather than guessing.

Can I dry filament with desiccant alone?

No. Desiccant keeps already-dry filament dry; it cannot pull meaningful water out of a wet spool at room temperature in a reasonable time.

Dry the spool in a heated dryer first, cool it, then seal it with fresh desiccant.

How do I know the drying cycle worked?

Three checks: the spool lost 2–5 g on a 1 kg roll, the popping sound at the nozzle is gone, and the extruded bead looks glossy instead of cloudy.

For critical parts, print a small layer-adhesion test before committing to a long job.

Which filament is the worst for moisture?

Nylon, including PA and PA-CF, absorbs the most and prints badly above about 0.2% water content. PC and TPU are next.

PLA is the most forgiving, which is why wet PLA often gets misdiagnosed as a slicer problem.