A filament can look clean, new and properly packaged while still containing too much moisture to print correctly. Many problems blamed on the slicer, nozzle or build plate actually come from wet material. The phenomenon is particularly visible with PA, TPU, PVA, PETG, PC and filled materials. Drying filament improves quality, but above all repeatability.

1. Why filaments absorb water

Some polymers are hygroscopic: they absorb water from the air. Nylon is the best-known example, but PETG, TPU, PC and many composites can also take on moisture. Absorption depends on the material, ambient humidity, exposure time and packaging.

2. What happens in the nozzle

When wet filament enters the hot nozzle, water turns into steam. This vaporization creates micro-bubbles, crackling, irregular extrusion and sometimes small pops. Flow becomes less stable, leading to rough walls, holes, stringing and poor layer cohesion.

3. Symptoms of wet filament

• Crackling or popping during extrusion.
• Matte, foamy or rough surface.
• Excessive stringing despite correct retraction settings.
• Intermittent under-extrusion.
• Reduced mechanical strength, especially between layers.
• Less regular dimensions on long or thin parts.

4. Impact on mechanical strength

Moisture does not only affect appearance. It disrupts melting and interlayer adhesion. A PA-CF part printed wet may look visually acceptable but lose a significant share of its strength. For functional parts, tooling, fasteners or components under load, printing dry material is a process requirement.

5. Drying: temperature and duration

Each filament has a drying window. Too low a temperature is ineffective; too high a temperature can soften the spool, fuse the windings or degrade the polymer. Follow the manufacturer recommendations and use a dryer, controlled oven or dedicated system. Domestic ovens are often inaccurate and risky.

6. Print from a dry box

Drying a spool and then leaving it open for several days cancels the effort, especially with nylon. For sensitive materials, print directly from a dry box or storage system with desiccant. Desiccant packs must be regenerated regularly or they become ineffective.

7. Drying and slicer profiles

Dry filament allows the slicer to be tuned more reliably. Retraction, temperature and flow settings become reproducible. Conversely, trying to compensate for wet filament with more retraction or less temperature often leads to unstable profiles. The first correction should be the material, not the software.

8. Simple workshop procedure

1. Identify moisture-sensitive materials and store them separately.
2. Dry before critical prints.
3. Print from a dry box.
4. Record opening date, drying date and conditions.
5. Visually check extrusion and surface quality on a test part.

Conclusion

Filament drying is one of the simplest levers for improving 3D printing. It reduces surface defects, stabilizes extrusion and improves mechanical strength. For technical materials, it is not optional: it is a material preparation step, just like machine calibration.

Machines-3D resources to go further

• professional FDM 3D printers
• Bambu Lab
• filament drying solutions
• PETG filaments
• contact a Machines-3D expert