Retraction is the slicer instruction that pulls filament back into the nozzle a small distance before the print head travels across open air. Without retraction, the hot plastic in the nozzle oozes out during travel moves and creates the thin stringy wisps between printed sections called stringing. Retraction is the primary control for stringing and is one of the most commonly tuned settings in FDM printing.
Retraction Distance and Speed
Two settings control retraction behavior: distance (how far the filament is pulled back) and speed (how fast it’s retracted). Direct drive printers like Bambu Lab machines need 0.4-1.0mm at 30-45mm/s. Bowden printers need 4-7mm at 40-60mm/s. The larger distance on Bowden compensates for compliance in the long PTFE tube between extruder and nozzle.
Too little retraction: stringing persists. Too much retraction on direct drive: the filament is pulled into the cold zone, causing partial clogs. On Bambu Lab printers, the default retraction settings in most PLA profiles are well-tuned and produce clean results without adjustment for standard materials. Tuning is needed when introducing a new filament brand or type with noticeably different flow characteristics.
The full stringing diagnosis and fix is at the stringing guide.
Frequently Asked Questions: Retraction in 3D Printing
What does retraction do in 3D printing?
It pulls filament backward into the nozzle before a travel move, reducing pressure in the melt zone so molten plastic doesn’t ooze out during the travel. This prevents or minimizes stringing between printed sections.
How much retraction do I need for PLA on a Bambu Lab printer?
The default Bambu Studio profiles for PLA are well-calibrated for retraction on Bambu hardware. For PLA, 0.5-0.8mm retraction at 35mm/s is a good manual starting point if you’re creating a custom profile. Tune with a stringing test tower if you see persistent stringing at default settings.
Can too much retraction cause problems?
Yes. Excessive retraction on direct drive printers pulls molten material into the heat transition zone where it cools and hardens, causing partial clogs. On Bambu Lab printers, keep retraction below 1.5mm. Over-retraction symptoms include clicking from the extruder and inconsistent extrusion starting after travel moves.
