Filament drying guide

How to dry filament without cooking it

Water inside your filament flashes into steam at the hot end: bubbles, voids, weak layers. Here's exactly how we dry PEEK, ULTEM, nylon and every other engineering polymer on our shop floor before every print.

See the method

Get the dry kit

Step 01 · Bake

70–140ºC

Per material

The day before you print. Check the data sheet.

Step 02 · Vacuum cool

Overnight

Oven off, vacuum on

The spool cools to room temp with no air around it.

Step 03 · Transfer

30–60 sec

Chamber to extruder

Straight into a preheated machine. No coffee break.

Step 04 · Check

1–2 ft

Of purge

Smooth and glassy? Print. Bubbles? Start over.

Printing PEEK, ULTEM or nylon?

Drying temperatures ›

Is it still wet? ›

Watch the video ›

The dry kit ›

Why it matters

Why does moisture matter for 3D printing?

Your print didn't fail because of your slicer, your machine or your part design. It failed because there's water in your filament.

Push wet filament through a 400ºC hot end and the water doesn't just evaporate. It flashes into steam. Steam inside molten polymer means bubbles and voids, which means weak layer adhesion and surface defects. Sometimes you don't find out until the print fails, or worse, the part fails in testing.

Absorbed moisture also acts as a plasticizer, lowering the glass transition temperature and strength of the plastic.

Most engineering polymers are hygroscopic: they actively pull water out of the air. Nylon is famously good at it, but it's not just nylon.

ULTEM · PEEK · Nylon · PPSU · PPS · Polycarbonate · ABS · PETG · PLA

The single biggest thing that separates a good print from a scrap part isn't the machine. It's how you handle the filament before it gets into the machine.

Wet vs. dry

Overhang quality

Wet filament leaves rough, sagging edges on the overhang. Dry filament holds a clean curve.

Wet vs. dry

Surface finish & texture

Steam pockets show up as pits and fuzz on the walls. Dry filament prints a smooth, even surface.

Hygroscopic plastics

The clock starts when the bag opens

A study on ULTEM 9085 found the filament reached an unacceptable moisture level within one hour of sitting out at room temperature. That's not the spool you forgot about for a week. That's the spool you took out of the bag this morning to print before lunch.

Our own testing on ULTEM and PEEK says the same thing: they soak up moisture in minutes, not hours.

Minutes

To re-absorb

ULTEM and PEEK, once the bag is open.

3–4 hr

Surface moisture

Comes out relatively fast.

24 hr+

Deep moisture

Absorbed deep into the material.

Heat + vacuum

Why baking alone doesn't work

You'd think you could crank up the oven, evaporate the water and be done. The whole game is getting the water out and leaving the polymer intact.

The problem

Heat degrades the polymer

Water boils at 100ºC at sea level. Pulling moisture from inside the filament, not just the surface, takes real heat and real time. Every minute at high temperature slowly breaks polymer chains down, until you have a spool that snaps every 2 feet on its way to the extruder.

The fix

Vacuum lowers the boiling point

Drop the pressure in a sealed chamber and you drop the boiling point of water with it. Pull a deep enough vacuum and water boils out at room temperature, so you can drive moisture out of the filament without cooking it.

Drying methods compared

Dehydrator, oven, vacuum or both?

Method

Hot enough for PEEK & ULTEM?

What goes wrong

Food dehydrator / consumer filament dryer

Usually not

Built for low-temp filament. Most don't reach the temperatures high-performance materials need.

Oven only

Yes

Long bakes degrade the polymer. Pull the spool out hot and it soaks moisture back up in open air.

Vacuum only, room temp

No heat

Slow. On its own it pulls out very little water.

Heat, then vacuum cool (our method)

Yes

Moisture boils off at lower temperatures, and the spool cools with no air to re-absorb from.

Our methodology

How we dry filament on our shop floor

The same process we use before every print of ULTEM, PEEK, PPS and polycarbonate for aerospace, defense and medical customers.

01

Bake

Bake the spool

The night before, or earlier in the day, put the spool you're going to print into the oven at the manufacturer's drying temperature.

Temperature: per data sheet
When: day before

02

Vacuum cool

Cool it under vacuum

About an hour before you leave for the day, turn the oven off and pull a vacuum on the spool. It cools to room temperature overnight with no air and no moisture around it.

Vacuum: full
Time: overnight

03

Transfer

Straight to the printer

In the morning, pull the spool from the chamber, walk it to the preheated machine, load it and start printing.

Chamber to extruder: 30–60 sec
Machine: preheated

04

Check

Read the purge

Watch the first purge closely. Smooth and glassy means print. Any bubbling means back to the oven and the vacuum.

Purge: 1–2 ft
Guide: Is it still wet? ›

Why

Hot polymer absorbs moisture faster than cold. A hot spool in open air is basically a sponge. That's why we never pull it out of the oven hot, and why the transfer takes seconds, not minutes.

Don't

Don't leave 17 spools in the oven for 2 weeks because you might use them eventually. We learned the hard way: the polymer degrades, gets brittle, and is almost not recoverable.

Drying temperatures

Filament drying temperatures by material

Starting points from our shop floor. Every material and every manufacturer is a little different, so check the data sheet for your spool.

Material

Oven temp

Vacuum cool

Notes

ULTEM 1010 / 9085

~120ºC

Every time

Much trickier than nylon. Do the full oven and vacuum cycle before you print.

PEEK

120–140ºC

Every time

Slower to absorb moisture, and slower to give it up. Once it's wet it takes even longer to dry, so plan ahead.

Nylon & CF nylon

~90ºC

Recommended

One of the easiest. It will dry overnight sitting in a heated printer chamber, like the 22 IDEX's.

PPSU, PPS, polycarbonate

Data sheet

Yes

Hygroscopic engineering polymers. Follow the manufacturer's drying temperature.

ABS, PETG & other lower-temp

~70ºC

Recommended

Lower drying temperatures, same process.

PLA

Below 70ºC

Optional

Still hygroscopic. Check the data sheet; some PLAs need lower still.

High drying temperatures can warp plastic spools. For PEEK and ULTEM we recommend metal spools.

How to tell

Is your filament still wet? Read the purge

Sometimes you think you dried it and it's not there yet. Before you walk away from a long print, watch the first nozzle purge right after you load the material.

Extreme

Steam

Actual steam coming off the nozzle and out of the extrusion.

Back to the oven

Medium

Little bubbles

Bubbles forming as the polymer flows out of the nozzle.

Back to the oven

Mild

The odd bubble

An occasional bubble instead of a smooth, glassy strand of molten polymer.

Back to the oven

Dry

Smooth & glassy

A foot or two of purge comes out perfectly smooth and beautiful.

Good to print

Popping at the nozzle

Steam escaping makes popping noises during printing, with visible gaps or bubbles in the part.

Rough walls & overhangs

Pits, fuzz and sagging overhang edges, like the wet-filament prints above.

Weak parts

Voids and poor layer adhesion. Sometimes you only find out when the part fails in testing.

Watch

You're drying filament wrong

Alt image

Chapters

1:14 Why moisture is the enemy

2:29 Why baking alone doesn't work

3:04 Why vacuum changes everything

3:35 The Vision Miner drying process

5:04 The 22 IDEX heated chamber

6:04 The dry kit vacuum chamber

6:54 How to read a purge

8:06 Nylon, ULTEM and PEEK notes
Alt image

Also watch

The 5.5 gallon vacuum chamber

A closer look at the bigger chamber: room for multiple spools, and it doubles as vacuum-sealed storage so dried filament is ready when you need it.

The dry kit

Get the drying gear

Already have an oven? Add the vacuum chamber and pump. Starting from scratch? The vacuum oven does the bake and the vacuum cool in one machine.

Add to your oven

Vacuum chamber + pump (5.5 gallon)

Not the vacuum chamber you find on Amazon. We had this one custom designed, extra large and in thick stainless steel, for drying high-temperature performance thermoplastics.

Fits big 5, 10 and 20 kg spools. Most chambers sold online can't.

Thick stainless steel. Customers have sent us photos of cheap chambers that imploded.

Vacuum pump included, for the vacuum-cool step

Doubles as vacuum-sealed storage between prints

$499.00

Pair it with any oven that can hold your material's drying temperature.

All in one machine

Vacuum oven, complete system

A vacuum drying oven with programmable step-up and step-down temperature control. Bake and vacuum cool in the same chamber, and use it for annealing parts too.

Programmable step-up / step-down temperature profiles

Bake and vacuum cool without moving the spool

Vacuum pump included

Doubles as an annealing oven for printed parts

$3,480.00

Oven and vacuum pump, ready to run the whole process.

Keep it dry while it prints

A 100ºC heated chamber that keeps filament dry

The 22 IDEX has a 100ºC actively heated chamber. Once the filament is in, it stays dry. No re-absorbing moisture mid-print and no quality drift on a 56-hour job. Warping is way better, and it handles huge, thick parts in PEEK, ULTEM, PPS, polycarbonate, ABS and nylon at full build volume.

See the 22 IDEX

10 yrs

Printing ULTEM & PEEK

Every day, for the last decade.

Production

Aerospace, defense, medical

Customers who test parts before they fly them.

COA / COC

On virtually every spool

Traceability for qualifying aerospace and medical parts.

833-774-6863

Talk to a real person

Right here in America. contact@visionminer.com

FAQ

Filament drying questions

How do I know if my filament is wet?

Watch the first purge when you load the filament. Steam coming off the nozzle means it's very wet. A stream of little bubbles means it's wet. An occasional bubble instead of a smooth, glassy strand means it's still slightly wet. Popping at the nozzle and rough, pitted walls are other signs. If a foot or two of purge comes out perfectly smooth, you're good to go.

What temperature should I dry PEEK, ULTEM and nylon at?

As a starting point: most ULTEM around 120ºC, PEEK 120–140ºC, nylon about 90ºC, lower-temperature materials around 70ºC, and PLA lower still. Every material and manufacturer is a little different, so check the data sheet for your spool. See the full temperature chart.

How long does it take to dry filament?

Surface moisture can come out in 3–4 hours. Moisture absorbed deeper can take 24 hours or more. We bake the day before, then let the spool cool under vacuum overnight so it's ready in the morning. PEEK is slow to give up moisture, so plan extra time.

Can I dry filament in a kitchen oven or food dehydrator?

Most food dehydrators and consumer filament dryers are built for low-temperature filament and don't get hot enough for PEEK, ULTEM or PPSU. Use an oven that can hold the material's drying temperature and is dedicated to filament. High temperatures can warp plastic spools, so we recommend metal spools.

Does vacuum drying work on its own?

Vacuum at room temperature on its own is slow and pulls out very little water. It works with heat. We bake the spool, then pull a vacuum while it cools, so moisture keeps boiling off and the spool can't re-absorb humidity from the air.

Can you over-dry or damage filament?

Yes. Every minute a polymer sits at high temperature it slowly degrades. Leave spools in the oven for days or weeks and they turn brittle, and that is almost not recoverable. Dry what you're going to print, not your whole shelf.
Why does my filament snap after drying?

It was most likely over-baked. Heat breaks polymer chains down slowly, until the spool snaps every couple of feet on the way to the extruder. Dry at the data sheet temperature, don't leave spools in the oven indefinitely, and use vacuum so you don't need extra heat.

How fast does dried filament absorb moisture again?

Fast. In our own testing, materials like ULTEM and PEEK soak up moisture in minutes, not hours. Hot filament absorbs moisture even faster than room-temperature filament, so never let a hot spool sit in open air. Move it from the vacuum chamber to a preheated printer in 30–60 seconds.

Do I need to dry PLA or PETG?

PETG, ABS, polycarbonate and even PLA are hygroscopic too. They dry at lower temperatures, around 70ºC or lower for PLA. Check the data sheet for your material.

How should I store filament after drying?

Keep it under vacuum until you print. The vacuum chamber doubles as storage. Otherwise store it sealed with desiccant. For the longest prints, a line of nitrogen or argon into the filament chamber at slight positive pressure forces oxygen and moisture out.

Does a heated printer chamber keep filament dry?

It helps a lot. The 22 IDEX has a 100ºC actively heated chamber, so filament doesn't re-absorb moisture mid-print, even on a 56-hour job. Nylon will even dry overnight sitting in the heated chamber.

What size spools fit the Vision Miner vacuum chamber?

The 5.5 gallon stainless steel chamber is extra large so it fits big 5, 10 and 20 kg spools, which most vacuum chambers sold online can't hold.

Highest-leverage fix

Dry it right before you touch a single setting

Drying filament right is the single highest-leverage thing you can do for print quality. It costs almost nothing. It just takes discipline, and that's the difference between aerospace-grade parts and a scrap bin full of expensive polymer.

Review the method

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