Why Is PETG So Much Harder to Print Than PLA?

PETG isn’t harder because you’re doing something wrong. It behaves differently from PLA: it’s more prone to stringing, it can stick to some build plates too well, and it picks up moisture from the air, which causes most of the strange surface problems people blame on settings. Start by drying the spool and using your slicer’s PETG profile, then work through the checks below.

Dry the filament first

Bambu Lab’s wiki lists PETG among the hygroscopic filaments it recommends drying before printing. It describes the signs of wet filament as popping sounds from the nozzle, bubbles while extruding, more stringing, rough surfaces, holes and weaker layer adhesion. If you’re not sure how a spool has been stored, Bambu Lab says to dry it.

Prusa’s drying table gives 55 °C for 6 hours for all versions of its PETG. It warns against going hotter, because the filament can soften and stick together on the spool, and says to stick to the listed times. Check your own filament maker’s numbers if they differ.

Drying also matters for calibration. Bambu Lab notes that damp filament makes Flow Dynamics (pressure advance) results unreliable, so dry the spool before you calibrate, not after.

Expect some stringing, and tune it down

Prusa’s PETG guide says plainly that PETG is prone to stringing. Its suggestions are more retraction and a slightly lower nozzle temperature, starting from the stock PrusaSlicer profile. Prusa’s stringing article suggests lowering the nozzle temperature by 5 to 10 °C to see if it helps, and trying a different spool, since one that has absorbed moisture will string a lot.

For reference, the Prusa guide lists 230 °C for the first layer and 240 °C after that, with the bed at 85 °C and then 90 °C. Those are Prusa’s numbers for its own printers and filament. Commenters on the article point out that newer PrusaSlicer profiles use higher temperatures, so treat your slicer’s current profile as the starting point.

Watch your build plate

PETG can stick to a smooth PEI sheet too well. Prusa’s guide says not to print PETG on smooth PEI because the adhesion may be too strong, and recommends a textured or satin sheet instead. If smooth PEI is all you have, Prusa suggests applying glue stick first. Bambu Lab owners should check which plates Bambu recommends for their PETG.

Go easy on the cooling fan

PLA likes a lot of cooling. PETG usually wants less. Prusa suggests running the part cooling fan off for the first few layers to avoid deformation, then at about half power. Prusa says cooling helps keep fine detail and reduces stringing, while turning the fan off gives the toughest parts. It also notes that for strong solid parts, adding perimeters works better than adding infill.

If it still isn’t right

Fine, detailed models are the hardest test. In a recent Bambu Lab forum thread about a lattice-shaped part in PETG, one reply suggested running pressure advance and flow calibrations for that filament, since thin features are very sensitive to those settings. That’s one user’s suggestion, but it matches the calibration advice in Bambu Lab’s own wiki.

The Prusa and Bambu Lab guides below cover each step in more detail.