Why Stringing Happens (And Why It Is Not Random)
Stringing occurs when molten filament oozes from the nozzle during travel moves — when the printhead moves from one feature to another without extruding. If you see fine hairs or blobs between features, the nozzle is dripping during those moves. It is a solvable problem, not a material defect. Here is how to fix it, material by material.
The Four Variables That Control Stringing
Filora PLA Filament 1KG
Pre-dried and diameter-controlled — less stringing right out of the box
1. Retraction Distance and Speed
Retraction pulls filament backward into the nozzle before a travel move, creating negative pressure that stops ooze. Too little retraction and the nozzle drips. Too much and you get clogs or underextrusion after the move.
Starting values by extruder type:
- Direct drive (Bambu, Prusa MK4, Voron): 0.5–2mm at 30–45mm/s
- Bowden (Ender 3, CR-10): 4–7mm at 40–60mm/s
By material:
- PLA: Direct 0.8–1.5mm / Bowden 4–6mm
- PETG: Direct 1–2mm / Bowden 4–6mm (PETG strings more — tune carefully)
- TPU: 0–0.5mm direct only (retraction causes jamming in flexible filaments)
- ABS/ASA: Direct 1–2mm / Bowden 4–6mm
- Nylon: Direct 1–2mm (minimize retraction, Nylon clogs easily with excess retraction)
2. Printing Temperature
Higher temperature means lower viscosity, which means more ooze. This is the most underrated stringing variable. If retraction is tuned and strings persist, drop temperature by 5°C increments and retest. Most stringing issues with PETG are temperature problems, not retraction problems.
Filora PETG Filament 1KG
Dialed-in PETG with minimal stringing at proper retraction settings
Temperature is also material-specific. PLA at 225°C when it prints fine at 210°C will string. PETG at 255°C when 235°C works will string badly. Print at the bottom of the recommended range before adjusting other settings.
3. Travel Speed
Faster travel means less time for the nozzle to drip during moves. Increase travel speed to 150–200mm/s minimum. Most slicer defaults are conservative here. A faster travel move is one of the easiest wins for stringing reduction. In PrusaSlicer, Bambu Studio, and Cura, travel speed is a separate setting from print speed — find it and push it up.
4. Combing Mode
Combing (called "avoid crossing perimeters" or "combing" depending on the slicer) routes travel moves over already-printed infill or perimeters rather than crossing open air above the build plate. When the nozzle travels over filled regions, small ooze deposits land on hidden surfaces instead of forming visible strings. Enable combing for most PLA, PLA+, and PETG prints. Disable it when travel speed is so high that ooze is already controlled.
Material-Specific Stringing Fixes
PLA Stringing
PLA with tuned retraction and temperature should produce minimal strings. If strings persist after hitting correct retraction: lower nozzle temp to 200–210°C, increase travel speed to 200mm/s, enable combing. Check filament for moisture — wet PLA strings even with perfect settings.
PETG Stringing
PETG is the most notorious stringer. Its low viscosity at printing temperatures makes it inherently prone to ooze. Fix sequence: first, lower temp (230–235°C instead of 250°C). Second, increase travel speed to 200mm/s+. Third, tune retraction upward in 0.3mm increments. Fourth, enable "wipe on retract" in your slicer. PETG stringing is almost always a temperature issue first.
TPU Stringing
TPU requires zero or near-zero retraction to avoid filament buckling in the extruder. Control stringing through temperature (220–225°C, minimum necessary) and fast travel moves instead. Combing mode is essential for TPU — route all moves over filled areas. Accept that some light stringing is normal with flexible filaments and easy to remove post-print.
The Systematic Approach
Do not adjust five settings at once. Print the same stringing test (a two-tower bridge test works well) and change one variable per run:
- Lower temperature by 5°C, retest
- Adjust retraction distance by ±0.5mm, retest
- Increase travel speed to 200mm/s, retest
- Enable and tune combing mode, retest
Most stringing problems resolve at step 1 or 2. When they do not, moisture in the filament is the hidden culprit — dry your spool at 45–50°C for 4–6 hours and retest from scratch.
When It Is Actually the Filament
Wet filament strings regardless of settings. If you have changed retraction, temperature, and travel speed with no improvement — especially on PETG or Nylon — pull the filament and dry it. Moisture-laden filament creates steam bubbles in the melt zone that force material out even under retraction pressure. This looks identical to a settings problem, and no slicer change will fix it.