One of the most common problems in 3D printing is wet filament. Many new users are surprised when they experience stringing, small bubbles, uneven surfaces, or poor layer adhesion – even if the printer is correctly calibrated.
In many cases, the cause is moisture.
Filament and Moisture Go Hand in Hand
When filament is produced, the molten plastic is typically cooled in a water bath during manufacturing. Although the filament is subsequently dried and packed with desiccant, it is almost impossible to completely avoid moisture.
At the same time, different types of plastic have varying abilities to absorb water from the air.
Some materials absorb very little moisture, while others act almost like a sponge. Materials such as Nylon, PVA, and TPU are particularly sensitive, but even PLA and PETG can absorb enough moisture to affect print quality.
What Happens Inside the Hotend?
When the filament is fed through the printer's hotend, it is typically heated to between 190°C and 300°C depending on the material.
The water inside the filament turns into steam in a matter of seconds.
This might sound harmless, but water expands about 1,700 times when it goes from liquid to steam.
This means that even very small amounts of moisture can create significant pressure inside the molten plastic.
When the filament is extruded through the nozzle, the steam tries to escape, which can disrupt the material flow.
Typical Signs of Wet Filament
If your filament contains moisture, you may experience:
- Stringing between printed parts
- Small bubbles or holes in the surface
- Uneven extrusion
- Clicking or popping sounds from the nozzle
- Poor layer adhesion
- Dull or rough surface
- Reduced print strength
The more moisture the filament contains, the more visible the problems become.
Why Does the Print Sometimes Start Fine?
Many people find that a print starts perfectly but develops flaws later.
This is often because the outermost part of the spool is relatively dry, while the moisture deeper inside the spool is still present.
As the printer reaches the more moist material, the errors begin to appear.
If this happens, it may be necessary to stop the print and dry the filament further.
The AMS Hygrometer Doesn't Tell the Whole Story
If you use an AMS or a filament box with a humidity sensor, it's important to understand what the reading shows.
The hygrometer measures the humidity in the box – not the moisture content inside the filament.
Therefore, a filament can still be wet, even if the humidity appears low.
When the filament is dried, moisture is gradually released into the air around the spool, after which desiccant or active drying can remove it.
How to Store Filament Correctly
To minimize moisture absorption, the following is recommended:
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Store filament in airtight bags or containers.
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Use silica gel or other desiccant.
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Dry filament before important prints.
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Store technical materials such as Nylon, PC, ASA, and fiber-reinforced filaments vacuum-sealed, or in a polydryer when not in use.
How quickly filament absorbs moisture largely depends on the environment. A dry living room provides completely different conditions than a damp workshop or basement.
Is a Filament Dryer Worth the Money?
For most 3D printer owners, the answer is yes.
A filament dryer typically costs far less than a printer or a failed large print job. Even filament that comes directly from a new and sealed bag can benefit from a drying cycle before use.
Therefore, one of the best habits in 3D printing is quite simple.
See our large selection of filament drying boxes here
If in doubt – dry the filament before printing.
It often only takes a few hours but can save many hours of troubleshooting later.