Retraction

Retraction is the slicer tool for preventing ooze during non-printing travel moves: it briefly pulls filament back to drop nozzle pressure, then re-primes before the next line. Aim for the smallest, gentlest retraction that stops strings and start/stop blobs; pushing distance/speed too far often causes restart gaps, chewed filament, or PLA heat-creep jams.

TL;DR

Tune retraction to stop stringing without causing restart gaps: start with a modest retraction distance for your drive type, then use temperature, travel speed, and wipe to finish the job instead of cranking distance.

A time sequence is the clearest way to see how retract, travel, and prime change nozzle pressure and why both strings and restart gaps happen.

What retraction changes inside the hotend

At the end of an extruded line, molten plastic in the nozzle is still under pressure. If the printer does a travel move with that pressure still present, plastic continues to ooze out, leaving strings between features and small blobs where motion pauses. Retraction reverses the extruder briefly to relax that pressure before travel, then pushes filament forward again (prime) so extrusion restarts cleanly.

Retraction settings you’ll see in slicers (what each one actually does)

Retraction distance controls how far filament is pulled back and is the main lever for reducing nozzle pressure during travel. Retraction speed controls how fast that pull-back happens; too fast can slip/grind, too slow may not reduce ooze before travel starts. Minimum travel distance prevents retracting on tiny moves to reduce wear, noise, and print time. Extra prime (restart) changes how much filament is pushed after a retract to rebuild pressure; too much makes a zit at the restart, too little makes a restart gap. Some slicers also offer wipe/coast options that change how the line ends, which can reduce end blobs without needing more retraction.

Starting points (typical ranges)

  • Direct drive: 0.2–1.5 mm retraction, 20–45 mm/s
  • Bowden: 2–6 mm retraction, 25–60 mm/s
  • Flexible filaments: shorter distance and gentler speed; filament compression makes the system “springy”
  • If you need extreme retraction to stop stringing, temperature, moisture, or travel planning is usually the real issue

Fast tuning workflow (reduce strings without hurting flow)

  1. Confirm basics: filament is dry, nozzle is clean, and nozzle temperature isn’t overly hot for that material.
  2. Print a real stringing test: at least two towers with clear air gaps and many repeated travels between them.
  3. Increase retraction distance in small steps until most strings disappear (direct: +0.2 mm; Bowden: +0.5 mm).
  4. If fine hairs remain, lower nozzle temperature 5–10 C and/or increase travel speed before pushing distance much higher.
  5. Adjust retraction speed only if needed: increase until it helps, but back off if you hear clicking, see filament dust, or see inconsistent extrusion.
  6. Fix restart quality last: restart gap means retraction is too much and/or extra prime is too low; restart zit means extra prime is too high and/or you need wipe/avoid-crossing-walls.

If retraction isn’t fixing it, check these first

Nozzle temperature
Hotter plastic is runnier and strings more; try -5 to -15 C before increasing retraction a lot.
Filament moisture
Wet filament can cause stringing and fuzzy hairs; drying often beats any retraction change.
Travel speed
Faster travel reduces ooze time; slow travel can string even with “correct” retraction.
Travel routing
Combing/avoid-crossing-walls can hide or prevent visible strings and zits by keeping travel inside the part.
Wipe / coast
Wipe reduces end blobs; coast can help but overuse causes end-of-line underfill.
Cooling
Stronger part cooling can reduce stringing on small features by solidifying ooze faster.

If you see this, try this first

Thin hairs between towers (especially PLA)

Likely cause: Plastic too hot and/or insufficient retraction for the setup

Fix: Lower nozzle temp 5–10 C; then increase retraction distance slightly

Blobs/zits at the start of a new line after travel

Likely cause: Too much extra prime and/or travel crosses visible outer walls

Fix: Reduce extra prime; enable wipe and/or avoid crossing outer walls

Gaps right after travel (restart gaps)

Likely cause: Retraction too aggressive, extra prime too low, or retraction too fast causing slip

Fix: Reduce retraction distance; add a small extra prime; slow retraction slightly if slipping

Extruder clicking, filament dust, or chewed filament

Likely cause: Retraction distance/speed too aggressive, high back-pressure, or heat creep

Fix: Reduce retraction distance and speed; check hotend fan and heatsink cleanliness

Stringing mostly on long travels only

Likely cause: Travel is slow, or retraction is skipped on shorter moves so pressure stays high until the long one

Fix: Increase travel speed; reduce minimum travel distance for retraction