Short answer
If it hisses or pops at the nozzle, the filament is damp. Dry the spool, store it in an airtight box with desiccant, and as a rule dry nylon before printing.
Damp filament: the short answer
Filament absorbs moisture from the air, and damp filament gives brittle parts, a rough surface, stringing and popping sounds during printing. The solution is to dry the spool in a filament dryer or an oven on low heat and then store it dry. How quickly it happens depends on the material: PLA lasts a long time, while nylon can become unusable within a few days in humid air.
Rule of thumb: If it hisses or pops at the nozzle, the filament is damp. Dry the spool, store it in an airtight box with desiccant, and as a rule dry nylon before printing.
How to recognise damp filament
The symptoms are easy to recognise once you know what to look for. It hisses, crackles or pops at the nozzle as the water turns to steam. The surface turns matte, rough or bubbly instead of smooth. Parts become brittle and the layers bond worse, and stringing increases markedly even with settings that used to work, something we go through in more detail in the guide to stringing. In the worst case you can even see small steam bubbles in the strand coming out of the nozzle.
How to dry filament
1. Filament dryer. A filament dryer is made for the job and keeps an even, low heat for several hours. Many models also let you print straight from the dryer, which is handy for materials like nylon that absorb moisture even during a long print.
2. Oven on low heat. An ordinary oven also works: put the spool in for 4 to 6 hours on low heat. Keep the temperature below the material's softening point, around 40 to 45 °C for PLA and around 60 to 70 °C for PETG, ABS and nylon. Use an oven thermometer: many ovens show the wrong temperature at low settings, and an oven that is too hot can deform both the spool and the filament. These are general guideline values that hobbyists have used for a long time.
3. Store it dry afterwards. Drying only helps if the filament is then kept dry. An airtight box or resealable bag with desiccant, such as silica gel, goes a long way. Colour-changing silica gel shows when the desiccant itself needs to be regenerated in the oven. Spools that are not in use should go straight back into the bag after printing.
How moisture-sensitive are different materials?
All filaments absorb moisture, but at very different rates. The table ranks the materials in our range.
More on nylon and PETG
For nylon, drying is not optional: the material can absorb so much moisture in a few days that parts become porous and swell. We describe the routine in How to print nylon, and for the string-prone PETG there is a corresponding walkthrough in How to print PETG.
Filament dryers: how to choose, and five models to compare
Not our own test. This is a compilation of the manufacturers' figures. We have not tried the models ourselves, and we do not sell any of them.
A filament dryer keeps the spool at an even, low heat for hours and is more convenient and more even than an oven, which often shows the wrong temperature at low settings. Five things decide which one suits you:
1. Maximum temperature. PLA is dried at 40–45 °C, but PETG, ABS and nylon need around 60–70 °C according to the guideline above. A model that tops out at 55 °C is enough for PLA but not for nylon, and falls below our guideline for PETG and ABS. The manufacturers' own presets differ somewhat from our guideline values, so read the manual for your particular filament.
2. Number of spools and spool size. Check that your spool fits (diameter and width), and whether you want to dry several at once.
3. Printing straight from the dryer. Nylon and TPU absorb moisture even during a long print, so a model that feeds the printer directly is worth a lot.
4. Power and timer. A simple single-spool model draws 35–50 W, while models for several spools draw several hundred watts.
5. Humidity meter. Some models show the humidity inside the box, but the measurement is rough: for the E2 the accuracy is stated as ±10 %.
Five models, according to the manufacturers' figures
Sources: eSUN for the eBOX Lite, Sunlu's manual for the S2, Creality for the Space Pi Plus, Sunlu for the S4 and 3druck.com's test for the E2. Power and dimensions differ between sources, so the figures are rounded: check them against the manual that comes with the dryer.
How to read the comparison.
- For PLA, all five will do. If you only print PLA, a simple single-spool model is usually enough.
- For PETG, ABS and nylon you need a model that reaches 70 °C, that is the S2, S4, Space Pi Plus or E2.
- The E2 reaches 110 °C and can therefore also be used to heat-treat finished parts, which 3druck.com covers in its test. That is overkill if you only want to dry filament.
- The S4 has room for four spools but draws the most power. That is more than you need if you dry one spool at a time.
Dryer or storage box?
They are not the same thing. A dryer heats and drives the moisture out of a spool that has already become damp. A storage box, such as Polymaker's PolyBox Edition II, does not heat: it keeps the air dry with silica gel, according to the manufacturer below 15 % humidity, so that dry filament stays dry. If your filament is already damp you need a dryer, and a box is good for spools you are not using right now.
Common questions about moisture and filament
How quickly does filament become damp?
It depends on the material and the humidity. Nylon can be affected within a few days in ordinary room air, TPU and PETG within a few weeks, while PLA often lasts considerably longer. In humid environments everything goes faster.
Can filament be ruined by moisture?
Usually not permanently: proper drying restores most of it. Filament that has been damp for a very long time can, however, become brittle in a way that cannot be dried out, especially PLA, which starts to be broken down by the water.
Do I need to dry brand-new filament?
Rarely. Spools are delivered vacuum-packed with desiccant and are dry on arrival. The exception is nylon, which may have absorbed moisture during a few days of open handling and therefore benefits from drying before the first important print.
What humidity should the storage box have?
Below 20 percent relative humidity is a good target for storage, and below 15 for nylon. A cheap hygrometer in the box takes away the guesswork.
Do I need a filament dryer, or is the oven enough?
An oven on low heat works for the occasional spool, but many ovens show the wrong temperature at low settings and can deform the spool. If you dry often, or print nylon and TPU, a dryer is more convenient and more even.
What temperature should a filament dryer reach?
For PLA, 40–45 °C is enough. For PETG, ABS and nylon it should reach 70 °C.
How long does it take to dry a spool?
Allow 4–6 hours at low heat, according to the oven guideline in this guide. Follow the manufacturer's times for the dryer you buy.
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