Drying 3D printing filament: why it matters and how to do it

Plastic filament pulls moisture from the air, and that moisture causes real problems. It sits inside the spool quietly until it hits the hot end at 200-plus degrees, where it flashes to steam. You hear it as a faint hissing or crackling. You see it as blobs, rough surfaces, excess stringing, and layer lines that look foamy rather than smooth. Parts come out weaker too — steam voids inside layers make a bracket snap where it should flex.

Drying is not optional for some materials. It is the first thing to check any time your print quality has mysteriously got worse.

Signs your filament has absorbed moisture

You do not need a moisture meter. The symptoms are fairly recognisable:

• Hissing or popping sounds from the nozzle during a print
• Blobs or zits appearing mid-print with no obvious cause
• Stringing much worse than usual, even with retraction tuned correctly
• Layer surfaces look rough, dull, or slightly foamy instead of smooth
• Thin walls are brittle and snap where they should flex
• PETG that is normally glossy coming out matte or chalky

Any one of these on its own might have another cause. Two or three together — especially with an old spool or one that has been sitting open — almost certainly points to moisture.

Which filaments absorb moisture fastest

Not all materials are equally affected. Here is a rough hierarchy from most urgent to least:

• Nylon (PA) — absorbs moisture extremely quickly. Always dry before use and keep it in a sealed container with desiccant even mid-print.
• PVA and BVOH — similar to Nylon. Ruins fast, often overnight.
• PC (polycarbonate) — needs high-temperature drying. Must be dry to print reliably at all.
• ASA and ABS — less dramatic, but benefit from drying if the spool is more than a few months old.
• PETG — very common and very susceptible. A few days open in UK humidity is enough to cause problems.
• TPU — wet TPU strings badly and loses elasticity.
• PLA — the slowest to absorb moisture, but spools stored in a damp workshop for six months or more will still show quality drops.

How to dry filament

Dedicated filament dryer

This is the easiest method. Units like the Sunlu FilaDryer S2 or the Polymaker PolyDryer Box hold a spool at a controlled temperature for as long as you need. Most let you print directly from the dryer while it runs, which is useful for Nylon. Set the temperature, set a timer, and walk away. They run from roughly £25 to £60. For anyone printing regularly, one pays for itself in saved filament fairly quickly.

Food dehydrator

A food dehydrator with a temperature dial works well. Most reach 35–75°C, which covers PLA, PETG, ABS, ASA, and TPU. One thing worth checking: does yours actually reach the temperature you set? A cheap unit can run 10°C low. A probe thermometer will confirm it. Also check your spool fits — standard 200 mm spools fit most mid-size dehydrators, but it is worth measuring before buying.

Kitchen oven

An oven works in principle, but it is the least reliable method. Most home ovens are inaccurate at low temperatures — 50°C on the dial might be 70°C inside, which will warp PLA. If you use this method, use an oven thermometer rather than trusting the dial. Do not use spools with cardboard hubs, as they deform. Leave the door slightly ajar so moisture can escape rather than cycling back into the filament.

How long does drying take

Drying time depends on the material and how wet it is. These are reasonable starting points:

• PLA — 4–6 hours at 40–45°C
• PETG — 4–6 hours at 65°C
• ABS / ASA — 4–6 hours at 60–70°C
• TPU — 4–6 hours at 45–50°C
• Nylon PA12 — 8–12 hours at 70–80°C (PA6 can need longer)
• PC — 4–6 hours at 80–90°C
• PVA / BVOH — 4–6 hours at 45–50°C

A spool that has been sitting open for months may need a second cycle. The tell is that print quality improves but hissing has not fully stopped — run it again.

Storing filament after drying

Drying is only half the problem. Leave a dry spool open and it will absorb moisture again — within hours for Nylon in a UK winter.

The most practical setup is a sealed plastic storage box with silica gel desiccant inside. Most silica gel changes colour when saturated, so you can tell when it needs recharging. Dry it in the oven at around 120°C for an hour to restore it. Vacuum bags work too and pack down well if storage space is tight.

For Nylon and PVA, the only really reliable solution mid-print is running directly from a sealed dry box or a dryer unit kept running for the duration of the job.

What drying cannot fix

Drying fixes moisture-related problems. If your filament has become brittle because it has been UV-exposed on a window ledge for a year, drying will not restore it. Brittle PLA that crumbles rather than flexing at all is degraded, not just damp — that spool is waste.

Similarly, if your quality problems are actually a blocked nozzle, a worn PTFE liner, incorrect temperatures, or a bed adhesion issue, drying will not help. Drying is the right first step because it is easy and costs nothing. But it is not a cure for everything.

When to get it printed instead

If you want something in a difficult material — Nylon, flexible TPU, or PC — and you do not have a dryer or the setup to keep it dry through a long print, it is worth letting us handle it. We print those materials regularly and keep them properly stored. If you just want parts without the hassle of managing moisture, upload your file at harktech.co.uk/printing.html, choose your material, and we will quote you based on weight and print time. Most orders turn around within a few working days.