3D print has thin strings between parts

Dry the filament first, then lower the temperature and tune retraction.

What the message means

Melted plastic oozes while the nozzle travels. Wet filament makes it worse and also gives a rough surface and popping sounds.

Fix it in this order

Dry the filament in a filament dryer or a low oven made for it, following the plastic maker advice.
Lower the nozzle temperature by 5 degrees at a time.
Increase retraction distance a little and check it works.
Raise the travel speed in the slicer.
Print a retraction test model to compare settings.
Store filament sealed with desiccant.

Why it happens

While the nozzle travels between parts of the print, melted plastic can still ooze out and leave a thin string. Retraction pulls the filament back a little to stop that, and a lower temperature makes the plastic less runny.

Many filaments take up moisture from the air. Water in the hot end turns to steam, which makes popping sounds and bubbles and lets plastic ooze more, so tuning retraction on wet filament gives poor results. Check your plastic maker’s advice for drying, because the safe temperature differs between materials.

If you see this, do this

You see	Do this
Strings and popping sounds	Wet filament.
Strings only	Temperature and retraction.

warping, wheel slip.

Last reviewed: November 2026. These are the usual causes and the order that finds them fastest. Test on your own board; clones and cables differ.

Why this happens

Filament leaves the nozzle because the melt inside it is under pressure and runny. When the head travels across an empty gap, that pressure and the low viscosity of hot plastic let a thread drip out. Retraction pulls the filament back to relieve the pressure, and a lower temperature thickens the melt so less of it escapes.

Moisture adds a second cause that settings cannot fully fix. Water absorbed by the plastic turns to steam inside the hot end, forms tiny bubbles and pushes extra plastic out during travel. Materials such as nylon, PETG, TPU and PVA take up water readily, and PLA can too if it sits open for weeks.

How to confirm the cause

Listen while a print runs. Crackling or popping at the nozzle points to moisture.
Extrude about 50 mm of filament in the air and look at it. Bubbles, a rough surface or a wisp of steam suggest wet filament; a smooth, glossy strand suggests dry filament.
Print a temperature tower or a two-pillar string test at several temperatures. If the strings thin out steadily as the temperature drops, heat is the main cause.
Dry the spool for the time and temperature your plastic maker recommends, then reprint the same file with no other change. If the strings disappear, moisture was the cause.
Change one setting per print and keep notes, otherwise you cannot tell which change helped.

Worked example

Example numbers only; use your own printer, plastic and slicer. A test with two thin pillars about 30 mm apart can be tuned like this.

Print 1: 215 C, retraction 1.0 mm, spool as it was  -> heavy strings, popping heard
Print 2: same settings, spool dried first            -> fewer strings, no popping
Print 3: 210 C, retraction 1.0 mm                    -> light strings
Print 4: 210 C, retraction 1.5 mm                    -> almost clean
Print 5: 205 C, retraction 1.5 mm                    -> clean, but check layer bonding
Rule: stop when the pillars are clean. Do not keep raising retraction.

Common mistakes

Changing temperature, retraction and speed together, so the result teaches nothing.
Raising retraction distance too far. Long retractions can pull molten plastic up into the cooler part of the hot end and cause clogs.
Lowering the temperature until layers no longer bond, which trades strings for weak parts.
Drying at a temperature that softens the spool, or drying in an ordinary kitchen oven that cannot hold a steady low temperature.
Tuning retraction on wet filament and then blaming the slicer.

If this did not fix it

Travel paths that cross open areas. Enable the slicer option that avoids crossing perimeters, so the nozzle travels over printed material.
A loose Bowden fitting or a gap at the tube end, which makes retraction move the filament without pulling the melt back.
A temperature reading that is wrong, so the nozzle is hotter than displayed. Check the thermistor setting and tune the heater.

3D print has thin strings between parts: retraction, temperature and wet filament