3D-Printing: How to Dry Wet Filament: PLA, ABS, Nylon & Co.

Martin

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Many filament types absorb moisture from the air. This makes them wet and can lead to errors during 3D printing. On the one hand, it is important to store the filaments properly and you should know how to dry them again once they have become wet.

To dry wet 3D printer filament, it is carefully heated to low temperatures. This allows the moisture to escape without the filament becoming soft and sticking together. To avoid wet filament, it must be stored in an airtight container with desiccant.

How you dry your filament, which temperatures are useful for this and whether you have to dry it at all, you will learn in this article. At the end of the article, I share with you my practical experience in before/after tests.

How can you recognize wet filament?

Wet filament produces typical printing errors. Here are signs that your filament needs to be dried: 

Bubble formation: If a filament has already absorbed a lot of moisture from the ambient air, bubbles can form during extrusion from the hot nozzle. The absorbed water boils away, evaporates and throws bubbles. 

Stringing: If the filament is only slightly damp and no bubbles are forming yet, stringing is one of the most important signs that the filament is wet. Especially if you notice that the frequency of stringing and its magnitude increase over time, there is definitely moisture in the filament.

Irregular layers: Due to the winding of the filament on the spool, parts of the filament are more susceptible to absorbing moisture from the air and some less. As a result, the absorption of moisture also varies along the length of the spool. This can result in very irregular layers. 

Brittle filament: Some filaments like PLA become brittle due to moisture. However, this process is fortunately very slow and it takes several months until the filament is unusable (depending on the humidity). Drying can restore the flexibility. 

Poor adhesion: The absorbed moisture can affect the print bed adhesion and also the adhesion of the individual layers to each other. For most filaments, other print defects such as stringing occur earlier than poor adhesion, but this effect is important when it comes to the strength of the object. 

Which filaments are particularly susceptible to moisture?

Some filaments suck more moisture from the air than others. This property is called hygroscopic. With some filaments, it is not necessary to dry them before each print. Others, on the other hand, only then deliver error-free results.

PETG, TPU, ABS, PC, nylon and PVA are among the filaments that are particularly hygroscopic. If they are stored in air, they quickly absorb moisture from the ambient air. In addition to dry storage (more on this later), some of these filaments only achieve error-free results if they have been dried before printing. 

Other filaments such as PLA are not quite as susceptible to moisture. They can also be processed flawlessly for several weeks without dry storage or active drying before printing. Over a longer period of time, however, PLA becomes brittle, which can lead to printing interruptions or clogging of the nozzle

Drying Methods

To dry wet filament, it must be heated to an elevated temperature so that the moisture inside can escape. A combination of heating and active drying is ideal.

Before we get into the individual temperatures and drying times, I’ll show you the most popular methods to dry wet filament.

Filament Dryer

The best way to dry wet filament is with specialized filament dryers. Although they are often the most expensive option, you will get the best results with such devices.

Filament dryers offer special programs for different filaments. This allows you to dry your filament at the touch of a button, without having to look up and manually enter the temperature and duration each time. Most filament dryers have a capacity of one spool, but some accommodate multiple spools.

A built-in heating coil slowly brings the filament to the desired temperature. The warm and moist air automatically escapes from the filament dryer. After the drying time, you can remove the dried filament and start printing immediately. 

Some filament dryers allow you to feed the filament from the inside through a small hole directly to the extruder of your 3D printer. For filaments that are particularly susceptible to moisture, you can avoid any moisture in this way. 

Especially for large objects made of PETG, nylon or other filaments that are very hygroscopic, such a filament dryer is useful. Even if you have dried the filament in an oven before printing, some of these filaments can become saturated with moisture again during the several hours or even days of printing. A direct feed from an active filament dryer prevents this. 

I am a big fan of the Sunlu FilaDryer S2. I have been using it for a very long time and mainly use it for PETG. Again, you can feed the dried filament through a hole directly to the 3D printer (as shown in the picture above). 

Oven

One of the easiest ways to dry damp filament is in an oven. Every household has an oven and it provides enough space to dry at least one spool of filament.

The disadvantage of an oven is that the built-in thermometers are often not very accurate and the actual temperature at the filament can deviate greatly. With filaments that already become soft at low temperatures, this can destroy the complete filament spool. PLA, for example, is very susceptible to elevated temperatures. The filament on the spool can then fuse so that it can no longer be unwound. 

It is best to place a suitable thermometer next to the filament to determine the actual temperature. Many ovens strongly overdrive. This can mean that the oven ends up at 70° for several minutes at the beginning of the process at a set temperature of 50 °C. 

For certain filaments like PLA, this would be fatal. So wait some time before you put the spool in and use an accurate thermometer. 

Food Dehydrator

If you don’t have a suitable oven or don’t want to hog it all the time, a dehydrator is a viable alternative. 

If you don’t have an automatic dehydrator, I would still advise you to buy a proper filament dehydrator. But maybe you can get hold of an older and cheap dehydrator that you can convert with little effort. On portals such as Thingiverse you can find many conversions for dehydrators. Perhaps you will find the right one for you. 

The disadvantage of dehydrators is that they can usually only take one coil and their temperature cannot be set very high. So for PLA and PETG, a dehydrator would be more suitable than for other materials that need higher temperatures. 

The advantage of dehydrators over ovens is that they are more mobile and can be placed right next to the 3D printer. In addition, the temperature accuracy is typically much higher and the temperature is also kept constant for a long time. 

Temperature & Duration

The temperature you use to dry filament varies greatly between filament types. If you choose too high a temperature, the filament can melt on the spool and become unusable.

FilamentTemperatureDuration
PLA45 °C> 5 hours
ABS80 °C> 5 hours
PETG60 °C> 5 hours
TPU45 °C> 5 hours
ASA80 °C> 5 hours
PC85 °C> 5 hours
Nylon80 °C> 5 hours
Temperature & duration for drying wet 3D printing filament.

Storage & Prevention

Ideally, you won’t need to dry your filament using any of the methods described above. If you have stored your filament dry, you can avoid a lot of moisture. Especially for less susceptible filaments like PLA, active drying is then no longer necessary.

For dry storage, you need an airtight container* that ensures dry ambient air. There are both options available for purchase and many ways to build such a dry storage space yourself. 

The principle is simple. You get an airtight container, put the spool and some desiccant in it and seal it. The desiccant is even more hygroscopic than the filament and absorbs moisture from the surrounding air. After some time, you will have to dry or replace the desiccant again. 

This keeps the air around the spool very dry for a very long time. The filament then has no chance of getting wet.

A suitable drying agent for this would be silica gel*. As an airtight container, you can use either a vacuum bag* or a suitable plastic box.

If you want to monitor the humidity inside, you can get a small hygrometer* and put it in the containers with you. This way you can always see at a glance how high the humidity is with the filament spool. 

Practical Test: Is drying filament worth it?

To test what effect drying filament has on the final result, I made the following comparisons: 

  • PLA snap test: PLA stored open for 1 year and stored dry for 1 year.
  • PETG Stringing: PETG stored dry and dried in a filament dryer before printing against PETG stored open for 2 weeks.

The snap test of PLA was pretty clear. The filament, which has been stored dry for a year, behaves just like a new filament. It is flexible and prints flawlessly.

The PLA filament, which was stored open for a year, broke after being lightly loaded. I also tried to print with it. The first 20 minutes went smoothly, but then the filament broke and printing was interrupted by the filament sensor. I was then able to reload the filament, but if it had broken in any other place, it could have clogged the nozzle. 

Wet vs. dry PETG filament.

PETG filament has a strong tendency to absorb moisture from the air. Therefore, this test was also much faster than the one with PLA filament. 

Even after a few days, the PETG filament absorbs so much moisture that the level of printing errors and their probability increases enormously. Especially, stringing is a big problem with PETG, particularly as soon as moisture is involved. 

The difference between the dry PETG filament and the open stored PETG filament is big. I was able to print the dry filament flawlessly, the wet filament produced a lot of stringing. 

Conclusion

If you notice the typical signs of wet filament, you can dry your filament using the methods described in this article. Be sure to store your filament in a dry place so that you can continue to print error-free in the future. 

If you 3D print frequently and you don’t just use your 3D printer sporadically, I highly recommend a filament dryer for the most vulnerable filaments. And regardless of what filament you use, you should store it in an airtight container with desiccant. 

Only if you print exclusively with PLA and use up the entire spool within a few weeks, you don’t have to worry so much about drying and storage.


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