Stringing and oozing

What does stringing actually look like, and how is it different from oozing?

Stringing is the fine, hair-like strands of plastic left stretched between two points on a print wherever the nozzle traveled without printing, most visible between separate parts or towers on the same plate. Oozing is the underlying cause showing up in a different spot: plastic slowly leaking out of the nozzle during a travel move or a pause, rather than being pulled back and held in place by retraction.

A print with heavy stringing usually also shows small blobs where a travel move started or ended, and sometimes a slightly rough, hairy texture on outer walls where oozed plastic got dragged across the surface. If cleanup with a heat gun or flame pass removes the strings easily and the rest of the print looks otherwise fine, stringing is the most likely diagnosis rather than a more serious extrusion problem.

Why is my nozzle leaking filament between parts?

The single biggest driver of stringing is nozzle temperature set higher than the filament needs. Molten plastic gets thinner and flows more easily as temperature rises, and past a certain point it becomes runny enough to seep out of the nozzle during a travel move even with retraction working correctly. This is why the same retraction settings that work fine at one temperature can produce heavy stringing a few degrees hotter.

The fix here is straightforward: lower nozzle temperature in small steps, five degrees at a time is a reasonable increment, and reprint a stringing test between each change until the strings mostly disappear. Going too low introduces its own problems, weak layer bonding and under extrusion, so the goal is the lowest temperature that still prints cleanly, not the lowest temperature possible.

Could wet filament be causing this?

Wet filament pops, strings, and prints noticeably weaker than the same spool would dry. Moisture trapped in the filament turns to steam the instant it hits the hot nozzle, and that steam disrupts the smooth flow of molten plastic on its way out, which shows up as popping sounds, small surface bubbles, and stringing that will not go away no matter how much temperature or retraction is adjusted. Nylon absorbs moisture faster than the other common filaments, but PETG and TPU are also meaningfully hygroscopic and can pick up enough moisture from a humid room in a surprisingly short time.

If stringing shows up on a spool that has been sitting open on a shelf, especially PETG, TPU, or nylon, drying the filament before changing anything else in the slicer is worth trying first. A dedicated filament dryer box holds a steady temperature below the material's melting point for long enough to drive out absorbed moisture, and vacuum-sealed storage bags with desiccant keep a dried spool from reabsorbing moisture between prints.

Is this a retraction setting problem?

Retraction distance and speed matter, but they are usually the third thing to check, after temperature and moisture, not the first. Retraction pulls molten plastic back into the nozzle before a travel move and pushes it back out afterward; if the distance is too short or the speed too slow, some ooze still escapes during the move even at a reasonable temperature with dry filament.

A direct-drive extruder generally needs a shorter retraction distance than a Bowden setup, because there is less distance between the extruder gear and the nozzle for the filament to compress into. If temperature and filament moisture both check out and stringing persists, increase retraction distance in small increments and confirm the improvement with a repeat test print rather than guessing at a single large change.

How do I fix stringing without breaking something else?

Work through the causes in order rather than changing several settings at once, since that makes it impossible to tell which change actually helped. Start by confirming the filament is dry, since a wet spool defeats every other fix. Then lower nozzle temperature in small steps until strings mostly clear up. Only after both of those are ruled out should retraction distance and speed be adjusted, and even then in small increments with a test print between changes.

Increasing travel speed, moving the nozzle faster during non-printing moves, also helps, because it gives less time for plastic to ooze out during the trip between two points. Most slicers separate travel speed from print speed, so this can usually be raised without affecting the surface finish of the print itself.

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