Brittle Filament

Printing with Carbon Fiber and Other Brittle Filaments

Fiber-reinforced materials such as carbon fiber (CF) and glass fiber (GF) composites offer excellent stiffness, strength, and dimensional stability, but they also tend to be more brittle on the spool than base polymers. This brittleness means certain precautions must be taken when handling and printing these materials to prevent filament breakage and ensure consistent extrusion.

Understanding Filament Brittleness

Some materials are naturally more brittle than others due to their polymer composition and the fiber content percentage. Fiber-reinforced filaments like Fiberon™ ASA-CF08 and PPS-CF10 are particularly brittle on the spool and require careful handling. Other blends may show better flexibility and feedability. The brittleness can be affected by storage conditions, manufacturing processes, or extended time under vacuum-sealed packaging that partially dehydrates the polymer.

Tips for Preparing Brittle Filaments

If your filament is snapping or showing signs of brittleness, there are a few steps that can help restore performance:

1. Dry the material before printing. Use a filament dryer or oven at the recommended drying temperature for several hours to remove absorbed moisture. Drying can improve layer adhesion and reduce snapping.

2. Remove the outer 50 grams of filament if the spool has been vacuum sealed for a long period of time. The outer winding can become more brittle due to long-term tension or dehydration.

3. If you receive a Polymaker spool that is too brittle to use right out of the packaging, please contact [email protected] for assistance.

Maintaining a Clean and Gentle Filament Path

The more brittle the filament, the less suited it is for multi-path feeding systems such as the AMS. Brittle materials should have a straight and unobstructed path to the extruder, avoiding sharp bends or kinks. Even small twists can create localized stress and cause the filament to snap. It is often better to feed directly from the spool without long PTFE tubes if possible.

Removing the top cover on certain printers, such as the Creality K1, can also allow the PTFE tube to move more freely and relieve tension on the filament. For Bambu Lab printers, users can follow the manufacturer’s PPA/PPS printing guide for additional handling advice: https://wiki.bambulab.com/en/h2/manual/PPA-PPS-printing-guide

Extruder Design and Compatibility

Some extruders apply more torque or filament bending during feeding, which can quickly lead to filament breaks. On the H2D printer, only the left extruder should be used when working with brittle filaments. The right extruder applies more stress, increasing the likelihood of snapping. Some other extruders may also struggle with stiff, fiber-reinforced filaments. Choosing an extruder design that minimizes twisting and provides consistent tension is key for smooth printing of brittle materials.

Additional Printing Recommendations

When printing with CF or GF-filled filaments:

• Use hardened steel or ruby-tipped nozzles to handle the abrasive fibers without excessive wear.

• Print at slightly higher temperatures within the recommended range to improve flow and layer adhesion.

• Reduce print speed by 25–50% for smoother extrusion.

• Ensure a gentle filament feed path, preferably using a direct drive extruder for greater control.

• Keep moisture under control, as even fiber-filled materials benefit from consistent drying.

By handling these materials carefully and optimizing filament routing, users can maintain feed reliability and produce high-strength, dimensionally stable parts even with the most brittle engineering-grade filaments.