Damp PETG or incorrect settings? How to tell the difference

Start with the symptoms—not by changing everything

PETG can string even when the filament is dry. The material naturally tends to ooze, so stringing alone is not enough to conclude that the spool has absorbed moisture. Prusa’s material guide lists both stringing and oozing as common PETG challenges. (help.prusa3d.com)

Moisture is more likely when several signs occur at the same time: the surface becomes rough or uneven, extrusion makes crackling sounds, small bubbles or blisters form, or the print repeatedly suffers from under-extrusion. Prusa’s filament-drying guide describes a degraded surface, bubbles, blisters, and weaker layer adhesion as possible effects of moisture. (help.prusa3d.com)

Troubleshoot in this order

1. Check whether the spool is actually dry

If the filament has been left exposed for a long time, stored in a damp place, or has started making crackling sounds during extrusion, drying it is a reasonable test. First, follow the manufacturer’s recommendation for that specific filament: different PETG blends may have different requirements.

For example, Prusa specifies 55 °C for 6 hours for its PETG variants. This is a specific recommendation for its materials, not a universal setting for all brands. Make sure the drying equipment maintains an even temperature and that the spool can withstand it. (help.prusa3d.com)

2. Change one print setting at a time

If the filament seems dry, or the problems persist after drying, troubleshoot the print profile. First, try lowering the nozzle temperature slightly, while staying within the filament manufacturer’s recommended range. Excessive temperature can contribute to oozing. Then try a small retraction adjustment and check whether print speed or cooling affects the result.

Make one change per test print. If you change the temperature, retraction, and speed at the same time, it will be difficult to tell which adjustment actually helped. Prusa recommends that PETG’s tendency to string can be countered, among other things, by adjusting retraction and lowering the nozzle temperature, but the right values depend on the printer and profile. (help.prusa3d.com)

3. Compare with a short test

Print a small model with several separate towers or posts. Compare a print made before drying with one made afterward, while keeping the same slicer settings. Don’t look only at the strings: also note the surface, small blisters, sounds from the nozzle, and whether the walls are even.

A better result after drying suggests that moisture contributed to the problem. If the crackling and blisters disappear but fine strings remain, you can continue fine-tuning the temperature and retraction. This is a practical troubleshooting method, not a laboratory test that reliably determines moisture content.

Prevent problems with dry storage

Don’t leave the PETG spool unprotected between prints. Store it in an airtight container or bag with desiccant, and seal the packaging immediately after use. Prusa recommends keeping filament in sealed storage with desiccant; a dry box can also help protect the material during printing. (help.prusa3d.com)

Remember the difference: desiccant in storage helps keep filament dry, while active heating is used when a spool needs to be dried. Always follow the material manufacturer’s temperature and time recommendations, and avoid using a regular kitchen oven if its temperature cannot be controlled reliably.

Quick checklist

• Just a little stringing? Start with temperature and retraction—PETG can ooze even when it is dry.
• Crackling sounds, blisters, or a rough surface? Suspect moisture and check the manufacturer’s drying recommendations.
• Did the print improve after drying? Store the spool in a more airtight place, protected from moisture.
• No clear improvement? Go back to the print profile and test one change at a time.

This way, you won’t waste time chasing retraction values to solve a moisture problem—or dry a spool when the temperature profile is what actually needs adjusting.