Wet Filament

3D Printing with Wet Filament: Causes, Symptoms, and Solutions

3D printing relies heavily on the properties of the filament you use. One common but often overlooked problem is the presence of moisture in filament. Many thermoplastics used in 3D printing are hygroscopic, meaning they absorb moisture from the air. Printing with wet filament can result in print defects, equipment issues, and wasted material. Understanding how moisture impacts your prints, recognizing the signs of wet filament, and knowing how to properly dry and store filament are all key to reliable 3D printing.

Why Moisture Causes Problems

Moisture absorbed by filament turns into steam when the filament is heated in the hotend. This steam can disrupt the extrusion process, causing a wide variety of print quality problems such as bubbling, poor layer adhesion, and an overall decline in structural and visual quality.

Signs of Wet Filament

These are some ways to tell if your filament has absorbed moisture:

• Print Quality Decline: Prints may have poor surface finish, roughness, bubbling, or weak, brittle layers. In PETG, this is easy to spot, and you can compare before and after drying results in the photos below.

• Excessive Stringing and Oozing: Wet filament creates stringier prints because steam causes inconsistent extrusion and little wisps between parts.

• Popping and Hissing Noises: If you hear pops or sizzling while extruding, that's water vapor escaping.

• Inconsistent Extrusion: Look for weakened, inconsistent, or even pitted extrusion.

• Uncertainty About Storage: If a spool hasn’t been used in a long time, it’s safest to dry it before printing.

PETG before and after drying

Hygroscopic Filaments: Not All Are the Same

Not all 3D printing filaments absorb moisture equally:

• Highly Hygroscopic: Nylon, PVA, TPU, and PETG are particularly prone to absorbing moisture. Drying is crucial for these, and often they need to be kept in a dryer even as they are being printed, especially in humid climates.

• Moderate Sensitivity: Filaments like ABS and some specialty copolymers benefit from periodic drying, especially if you live somewhere humid.

• Low Sensitivity: PLA is less likely to be affected, but can still take on moisture over time or in damp conditions.

Living in humid environments greatly increases the risk of moisture absorption, making moisture control and drying routines much more important.

How Polymaker Handles Moisture: Pre-Drying Before Shipping

Polymaker pre-dries every spool before packaging and shipping. Each spool undergoes a controlled drying process, using precise heat and airflow to eliminate absorbed moisture. After drying, the filament is vacuum-sealed with a desiccant pack in an airtight bag. This prevents additional moisture uptake during shipping and storage. That way, when you open a newly purchased, vacuum-sealed Polymaker spool, you can expect it to be dry and ready for immediate printing, provided the seal is intact. This approach is especially important for sensitive materials like nylon, but Polymaker applies these high standards across all their filaments.

How to Dry Filament

If your filament has become wet, or if you suspect it has, here are some ways to dry it:

• Filament Dryers: Specialized filament dryers, such as the PolyDryer by Polymaker, are effective and convenient. They combine heat and airflow to drive out moisture and can often be used to both dry and store filament, or even feed filament directly to your printer.

• Convection Ovens: Household convection ovens can work if you set them at a low, stable temperature. Airflow is important for efficient drying; without good air movement, it may take longer or require higher temperatures.

• Food Dehydrators: These provide both heat and airflow and can dry smaller spools effectively.

• DIY Dry Boxes: Airtight containers with desiccant packs are good for storage after drying but are less effective for active drying.

Always follow the recommended drying times and temperatures for your specific filament type to avoid damaging or deforming it.

Keeping Filament Dry

Once dried, keep your filament in airtight bags or dry boxes with desiccant, or use vacuum containers. Avoid letting filament sit exposed, especially if you are not actively printing. Modular storage systems, such as the PolyDryer, help keep filament ready for use and allow you to print directly from a dry environment.