Stringing is the web of fine plastic strands left when the nozzle travels across an open gap. A small amount of wispy material can be removed easily, but heavy strands usually mean molten polymer is escaping during travel moves.
Quick diagnosis
Before changing retraction, make sure the defect really is stringing.
| What you see | More likely explanation |
|---|---|
| Fine hairs between two towers or separate features | Stringing or oozing |
| Small bumps concentrated where each layer begins | Seam or blob issue |
| A dragged line across a top surface | Travel path or nozzle collision |
| Rough flow with popping or bubbles | Moisture may be involved |
| Missing lines after aggressive retraction changes | Under extrusion or a developing clog |
The last two rows are clues, not proof. Moisture, temperature, residue, and flow problems can overlap.
Most common causes
- The nozzle is hotter than this filament needs. Lower viscosity makes it easier for plastic to leak during travel. Pigment, additives, flow rate, and hotend design all affect the useful range.
- Retraction does not suit the extruder and hotend. Too little may leave pressure in the nozzle; too much can grind filament or pull softened plastic into a cooler area.
- The filament has absorbed moisture. PETG, TPU, and other hygroscopic materials can show more surface defects when wet, but stringing alone does not diagnose moisture.
- Plastic is stuck to the nozzle exterior. Residue can be pulled into strands even when the slicer settings are reasonable.
- Travel choices cross open areas. Some slicers can keep more travel inside printed boundaries or wipe before moving.
Fix 1: restore a known-good profile
What to check
Confirm the printer model, extruder type, nozzle diameter, and material preset in the slicer. If you recently swapped from a 0.4 mm to a 0.6 mm nozzle, old G-code is no longer a valid baseline.
Why it happens
A profile can quietly carry unusual temperature, retraction, flow, or travel values from an earlier experiment.
How to correct it
Select the manufacturer-supplied or otherwise validated preset for the exact hardware. Re-slice the test model. Do not simply reset one visible field; inherited overrides can remain elsewhere.
How to verify
Print the same two-tower stringing test with the same spool and environment. If the defect falls sharply, compare the old and restored profiles before making another change.
Fix 2: inspect the material and nozzle
Secure the spool so it turns freely. Look for dust on the filament and burnt or stringy residue on the nozzle. Clean the nozzle exterior only at the temperature and with the method approved for your hotend; keep tools away from heater and thermistor wires.
If the filament pops, bubbles, feels unusually brittle, or produces a rough surface, dry it using the supplier’s temperature and time. A sealed box helps keep dry filament dry, but passive desiccant may not restore a spool that has already absorbed significant moisture. See how to store filament for a simple system.
Fix 3: tune nozzle temperature
Start at the preset value or the filament maker’s stated range. Lower the nozzle temperature by about 5°C per test, staying inside the supported range. Use identical test geometry and do not change fan speed, retraction, or travel at the same time.
Look for a balance: fewer strands without weak layer bonding, a rough matte surface, feeder clicking, or incomplete lines. A temperature that looks clean on a slow test may be too low for a fast, high-flow part.
Fix 4: tune retraction carefully
Retraction briefly pulls filament back before a travel move. The useful distance and speed depend heavily on whether the machine is direct drive or Bowden, the hotend’s melt-zone geometry, and the material.
- Begin with the printer profile’s value.
- Run a retraction test that changes only one parameter.
- Make small adjustments within the printer or hotend maker’s documented limits.
- Stop if the feeder grinds, extrusion becomes inconsistent, or a clog develops.
Fix 5: review travel and wipe options
Once temperature and retraction are sensible, inspect the slicer’s travel preview. Options named “avoid crossing perimeters,” “combing,” “wipe,” or similar can reduce visible travel across open space, but their behavior differs by slicer. Read that slicer’s documentation and watch for longer travel times or surface marks.
How to verify the fix
Use the same small two-feature model for every test. Record the profile name, temperature, retraction distance and speed, travel option, and result. Success means substantially fewer strands without new gaps, weak walls, grinding, or a clog.
If flow becomes intermittent, switch to the under-extrusion checklist. If purging is weak even with a stock profile, diagnose a possible clogged nozzle.
Use a comparison that includes restart quality
Photograph the gap between test features and the first extruded line after each travel. Label each sample with its one changed setting. A sample with fewer threads but missing restart lines has traded defects rather than solved the job. Repeat the chosen profile on a small section of the real model, because travel distance and cooling time differ from a two-tower test. If results vary across identical repeats, check the material condition and filament path before continuing to increase retraction.
Source and scope
The diagnostic order is consistent with Prusa’s official stringing and oozing guidance. Exact temperatures and retraction limits must come from the documentation for your filament, printer, and hotend.