When PETG pops or hisses at the nozzle and leaves bubbles or a rough, foamy surface, the cause is almost always water in the plastic. PETG soaks up moisture fast, and that water boils the moment it hits the nozzle, so it pops and blows bubbles into the print. Bambu’s wet-PETG guide is blunt about it: dry the spool and the popping stops.
This is a moisture problem, not a slicer problem, so the fix is drying and storage, not a setting change. Dry it once, then keep it dry.
Per Bambu’s PETG page, dry PETG at 60 to 65 C for about 4 to 8 hours to pull the water back out.
The causes, ranked
| Likely cause | Fix | Severity |
|---|---|---|
| Wet PETG | Dry the spool at 60 to 65 C for 4 to 8 hours, then reprint. | hi |
| Spool left open | Store the spool sealed with desiccant the moment a print ends. | hi |
| Printed in a humid room | Print the PETG straight from a filament dryer so it stays dry. | md |
| Old or hygroscopic spool | Dry the PETG before every long print, since it re-wets fast. | md |
| Storage desiccant spent | Recharge or replace the desiccant so the bin stays dry. | lo |
First fixes to try
Dry the spool, then check the signs against a fresh print.
Dry the PETG
Run the spool at 60 to 65 C for 4 to 8 hours in a filament dryer or food dehydrator.
Reprint and listen
Print a small part and listen for popping, then look for bubbles or a foamy surface.
Print from the dryer
Feed the PETG straight from the dryer so it cannot re-wet during the print.
Store it sealed
Put the spool in an airtight bag or bin with desiccant the moment the print ends.
When quick fixes are not enough
When one dry does not hold, the storage is the next thing to fix.
Refresh the desiccant
Recharge or replace the desiccant, since spent beads let humidity climb back into the bin.
Add a hygrometer
Put a small hygrometer in the storage bin so you can see when the humidity rises.
Dry longer for bad spools
A spool left open for weeks may need a second 4 to 8 hour dry to fully clear.
How PETG differs
PETG pulls in moisture faster than PLA and far faster than ABS, so a spool left out a few days in a humid room can already pop. PLA tolerates more open-air time, and nylon is the only common filament that drinks water faster than PETG. Dry PETG at 60 to 65 C, since hotter heat can soften or warp the spool.
Mistakes that keep PETG popping
A few choices dry the spool once and let it go wet again.
Avoiddo not
- Drying the spool, then leaving it open on the printer.
- Storing PETG with spent desiccant, which holds moisture in.
- Blaming the nozzle temp for popping before you dry the filament.
- Printing PETG from a humid room with no dryer.
Key takeaways
- PETG pops and bubbles from water that boils at the nozzle.
- Dry the spool at 60 to 65 C for 4 to 8 hours.
- Print from a dryer and store the spool sealed with desiccant.
- PETG absorbs moisture faster than PLA.
For the wider write-up, the wet filament guide covers any material, and the filament storage guide covers the sealed-container setup.
Related guides
Related
More in this area
Cross-reference
Sources & methodology
3 citations · reviewed 2026-07-10- 01Bambu Lab Wiki: Printing wet or undried PETG (popping and drying)accessed 2026-07-09Tier 1
- 02Bambu Lab PETG Usage Guide (wiki): PETG drying valuesaccessed 2026-06-29Tier 1
- 03All3DP: How to dry filament (PLA, ABS, nylon)accessed 2026-07-09Tier 2