Yes, PETG is hygroscopic, meaning it actively pulls moisture from the surrounding air. In a typical indoor environment with 50% to 60% relative humidity, PETG filament absorbs roughly 0.07% of its weight in moisture within 24 hours and about 0.10% within a week. Those numbers sound tiny, but even that small amount of water can noticeably degrade your prints.
How Quickly Moisture Becomes a Problem
The speed of absorption depends heavily on your local humidity. In moderate conditions (55% to 60% relative humidity at around 21°C), some users report printing from a freshly opened spool for a week or more without obvious issues, while others notice increased stringing after just a few days. In one well-documented case, a printer saw serious quality deterioration by the end of a ten-hour print session that started with freshly dried filament in a humid room.
The practical takeaway: PETG doesn’t go bad overnight, but it’s far less forgiving than many people expect. If you’re printing a multi-day job or live somewhere humid, the filament sitting on your spool holder is getting wetter the entire time.
How PETG Compares to Other Filaments
PETG falls in the middle of the moisture sensitivity spectrum for common 3D printing materials. It absorbs more water than PLA and significantly more than ABS, but far less than nylon, which can lose over half its strength when saturated. TPU is also highly moisture-sensitive, absorbing water quickly.
- PLA: Low to moderate sensitivity, absorbs slowly
- ABS: Moderate sensitivity, barely absorbs moisture in practice
- PETG: High sensitivity, moderate to fast absorption
- TPU: High sensitivity, fast absorption
- Nylon: Very high sensitivity, absorbs very fast
Despite absorbing more moisture than PLA, PETG still performs well in humid environments overall. It doesn’t break down from heat and humidity the way PLA can. The issue is specifically about print quality rather than long-term material degradation.
What Wet PETG Looks and Sounds Like
The single most obvious sign is sound. When moisture trapped in the filament hits the hot nozzle and flashes into steam, you’ll hear popping, crackling, hissing, or sizzling. If your printer suddenly sounds like it’s frying something, your filament is wet.
Visually, wet PETG produces a constellation of defects. Steam bubbles form inside the extruded plastic, leaving pinholes, tiny craters, and a rough or grainy surface texture. The expanding steam also pushes molten plastic out unevenly, causing thin strings between parts of the print, blobs on corners, and dripping on bridges.
The structural damage is less visible but more consequential. Steam trapped between layers prevents them from fusing properly, so printed parts come out weak, brittle, and easy to snap. You may also notice random thin layers, missing walls, or holes in the perimeter where disrupted extrusion flow left gaps. A part that should be solid and tough ends up feeling soft or fragile.
How to Dry Wet PETG
PETG has a glass transition temperature of 80 to 85°C, which is the point where it starts to soften. That gives you a comfortable margin for drying. The widely recommended setting is 55°C for about 6 hours. This is warm enough to drive out absorbed water without risking any deformation of the filament on the spool.
You can dry PETG in a dedicated filament dryer, a food dehydrator, or a conventional oven set to a reliable low temperature. Ovens can be tricky because many home ovens fluctuate by 10 to 15 degrees, and overshooting toward the glass transition temperature could fuse layers of filament together on the spool. A filament dryer or dehydrator with accurate temperature control is the safer choice.
Slowing your print speed can also help compensate for mild moisture contamination by giving the filament more consistent extrusion. But this is a workaround, not a fix. Drying the filament first produces far better results.
Storing PETG to Prevent Absorption
For long-term storage beyond a few months, keep PETG below 20% relative humidity. Vacuum-sealed bags with silica gel desiccant packets are the simplest approach. Airtight plastic containers with a tight-fitting lid and desiccant work well too. A small hygrometer inside the container lets you verify the humidity stays low.
For short-term storage of a few weeks, 40% relative humidity is generally acceptable for PETG. The filament will absorb some moisture, but not enough to cause dramatic problems if you’re actively printing through the spool. The longer the storage time and the higher the ambient humidity, the more water the material takes on, so the threshold tightens as the timeline extends.
If you’re printing from a spool that’s been sitting out for more than a week in a humid room, a quick drying cycle before your next print is cheap insurance against wasted time and failed parts.