GLOSSARY
Retraction
Retraction is the slicer telling the extruder to pull the filament back a few millimeters before any travel move. It relieves nozzle pressure so molten plastic stops oozing out — preventing strings.
Definition
When the toolhead moves between two extrusion points without printing, residual pressure in the nozzle pushes melted plastic out, leaving a fine string between the two points. Retraction reverses the extruder by a configured distance and speed immediately before each travel move, then re-pushes when extrusion resumes.
Two values matter: distance (how far to pull back, typically 0.5–2mm on direct-drive, 3–6mm on Bowden) and speed (how fast, typically 25–60 mm/s).
Why it matters
Stringing is the most common visual defect on FDM prints. Tuning retraction is the fastest way to clean up surface quality without changing anything else. Most slicer profiles include a sane default; calibration prints (the "retraction tower" or "temperature tower") help you fine-tune for your specific filament.
Common confusion
Stringing is not always retraction's fault. Wet filament strings even with perfect retraction settings — the moisture flashes to steam in the nozzle and disrupts flow. Dry the spool before tuning further.
Excess retraction wears out the extruder gear and can cause jams, especially with TPU or other flexible filaments. If a material persistently jams during retraction, reduce distance or turn retraction off.