PETG is usually recommended as the low-warping middle ground between PLA and ABS — yet its corners still lift when the bed is too cool or a draft hits the part. The fix is smaller than for ABS, but it is not zero.
Why PETG corners lift
Polymaker's PETG guide puts it plainly: PETG does not warp as aggressively as ABS, but a heated bed is still recommended to prevent lifting. The underlying cause is the same one Simplify3D describes for warping in general — plastic shrinks as it cools, and each layer contracts slightly more than the one below it, pulling the corners up (warping guide).
The bed temperature that holds it flat
Set the bed to 70–85 °C and the nozzle to 220–260 °C, the ranges Polymaker lists for PETG (PETG guide). A bed at the cool end of that range is usually enough, but if a corner still lifts, raise it within 70–85 °C before changing anything else. For the build surface, Polymaker recommends glue sticks, painter's tape, or PEI sheets to strike the balance between parts that detach and parts that fuse to the bed.
First layer, cooling, and drafts
Lay the first layer down slowly. Polymaker recommends a 20–30 mm/s first layer to improve bed adhesion, and notes that a silicone nozzle sock helps keep stray filament from building up and dragging across the print (PETG guide). Simplify3D's bed-adhesion guide adds two first-layer rules that help prevent lift: print the first layer slower so the plastic has time to bond, and keep the part out of drafts so the corners do not cool unevenly. If the corners curl on small features specifically, Simplify3D's curling guide points to cooling that is too slow for the detail.
A five-minute test
Print a single-layer square with sharp corners, then a small box. If the square's corners stay flat and the box's base does not peel as it grows, the bed and first-layer settings are right. If a corner lifts, add a brim as Simplify3D recommends for parts that still curl, and keep the bed in the 70–85 °C range rather than chasing the nozzle.
FAQ
Does PETG warp as much as ABS?
No. Polymaker ranks PETG's warping as lighter than ABS, which is why a heated bed is recommended but an enclosure is usually not required (PETG guide).
Why do PETG corners lift on some printers but not others?
Usually it comes down to bed temperature and drafts. A bed at the cool end of the 70–85 °C range plus a drafty room is enough to lift a corner on a large flat part, even though PETG is forgiving.
Is PETG heat-resistant enough for outdoor parts?
Polymaker lists PETG as withstanding temperatures up to 80 °C — above PLA but below ABS/ASA — and its own page recommends PETG for outdoor and UV-exposed parts such as garden tools and signage (PETG guide).