PETG: stringing, plastic stuck to the nozzle and parts that grip the plate too hard

Symptom

With PETG the part has strings and blobs, plastic builds up around the nozzle and then leaves marks or gaps in the part, or the part sticks so hard to a smooth PEI plate that removing it tears the surface.

Likely causes, from most to least likely

1. Damp filament: PETG absorbs moisture from the air; when heated, the steam pushes molten plastic outwards, where it sticks to the nozzle and leaves strings and a rough surface.
2. Temperature not matched to speed: printing slowly without lowering the temperature makes the plastic very runny and it oozes; too cold, on the other hand, and layers separate.
3. High flow ratio: Bambu Lab puts PETG between 0.93 and 0.96; above that, more oozing and more plastic on the nozzle.
4. Many travel moves, little retraction or too little cooling: PETG naturally tends to string.
5. A worn nozzle or a nozzle wiper in poor condition that does not clean it.
6. Smooth PEI plate without a release layer: Prusa warns adhesion can be strong enough to damage the plate.

Checks to tell which one it is

• Purge a little: if the filament comes out with bubbles or popping, it is damp.
• Compare your profile's temperature and flow with the filament maker's values.
• Look at the hot nozzle tip without touching it: stuck plastic or wear.
• Check which plate you use: for PETG, Prusa recommends the powder-coated textured or the satin sheet.

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

1. Dry and store the PETG

   Dry the spool before printing at the temperature and time on its label (Creality gives 60-65 °C for 4-6 h for its CR-PETG) and then store it sealed with desiccant. Bambu Lab recommends storing it below 20% relative humidity.

   Check: No more bubbles when purging and fewer strings.

   If that does not fix it: Adjust temperature and speed (next step).

2. Adjust temperature and speed

   Start from the maker's profile: Prusa uses 230 °C for the first layer and 240 °C for the rest, with the bed at 85 and 90 °C. If there are strings or blobs, lower the nozzle by 5-10 °C, and lower it too if you reduce the speed or the maximum volumetric speed. If layers separate, you are printing too cold.

   Check: Fewer strings and layers still bond well.

   If that does not fix it: Adjust flow, fan and retraction (next step).

3. Flow, fan and retraction

   With dry filament and blobs on the nozzle, lower the flow ratio to 0.93-0.94 (do not exceed 0.96). Try lowering the maximum volumetric speed by 4-5 mm³/s and raising the fan by 10-20%. Increase retraction slightly, staying under 2 mm (the rule Bambu Lab gives for its printers): too much retraction can clog. Arrange parts to avoid long travel moves.

   Check: The nozzle stays clean during the print.

   If that does not fix it: Clean or replace the nozzle (next step).

4. Clean or replace the nozzle

   Heat the nozzle and carefully remove the built-up plastic (it is hot). If it is worn, replace it. If your printer has a nozzle wiper, check it is not worn, loose, too low or broken.

   Check: The tip is clean with no visible wear.

   If that does not fix it: Check the plate if the problem is excessive adhesion (next step).

5. Stop it gripping the plate too hard

   Print PETG on a textured or satin plate. If you use smooth PEI, apply glue stick first as a release layer. Creality also suggests raising the Z offset by about 0.05 mm compared with PLA and printing the first layer at 20 mm/s or less.

   Check: The part releases without damaging the surface.

   If that does not fix it: If the plate is already damaged, ask your printer's maker whether it needs replacing.

Prevention

• Store PETG sealed with desiccant and dry it if it has been left out.
• Do not print PETG straight onto smooth PEI: use a textured or satin plate, or glue as a release layer.
• If you lower the speed, lower the temperature too.

Still not fixed?

Tell usi3d's AI about your case: choose your printer, describe what you see and add photos if you like. It proposes checks step by step, with their sources.

Tell the AI about your case

Printers it applies to

Any FDM (filament) 3D printer, from any brand.

Material: PETG.

Official sources

This guide summarises the official documentation linked here:

• PETG (material guide) · Prusa Research
• The filament sticks to the nozzle · Bambu Lab
• CR-PETG · Creality
• Guide to FDM Printing Filament · Elegoo