Corners Curling Up Off the Bed (Warping)

Likely causes, most common first

1. Bed temperature too low, or the wrong plate selectedMost common
   The same filament is printed at different bed temperatures on different plates, so the wrong plate setting gives a bed that is too cool. Bambu Lab adds that on its printers the plate choice also changes the nozzle height after leveling (its Textured PEI Plate setting lowers the nozzle by 0.04 mm Maker spec), so the wrong choice also weakens the first layer.
2. Too much part cooling, especially earlyVery common
   Fast cooling builds stress between layers. Bambu Lab recommends no cooling for the first 3 layers on most common filaments Starting point. Prusa notes that too much fan can lift the whole object and weaken layer bonding.
3. Cold room or draftsCommon
   Prusa says open windows and nearby air conditioners increase warping. Bambu Lab notes that below about 20 °C room temperature Rule of thumb even PLA and PETG warp, and that an open-frame printer leaves the part at room temperature.
4. A high-shrink material printed without heat around itCommon
   Prusa says warping is most common with high-temperature materials such as PC Blend, ASA and ABS, because of the large gap between nozzle temperature and room temperature. Bambu Lab adds PETG and PA (nylon) to the list of filaments that warp more easily than PLA.
5. Dirty or greasy plateCommon
   Oil from fingers lowers adhesion everywhere, so the corners give up first. Prusa recommends wiping the surface with 90% or stronger isopropyl alcohol Maker spec on its sheets.
6. Large part with dense infillOccasional
   Bambu Lab says large models with high infill density shrink more, that infill patterns with more straight lines shrink more than gyroid, and suggests staying under about 50% infill Rule of thumb to reduce shrinkage.
7. Printing fastOccasional
   Prusa suggests lowering print speed for high-warp materials so layers settle and fuse better.

Fix it, one change at a time

1. Fix the plate and bed settings first. Select the plate that is really on the printer, use the bed temperature range on the filament label, and start from the slicer's stock profile for that filament. Prusa and Bambu Lab both say their stock filament profiles are already tuned.
2. Clean the plate with high-strength isopropyl alcohol, or as the plate maker instructs, and handle it by the edges.
3. Turn off part cooling for the first few layers (the slicer setting is often called something like "no cooling for the first layers"). If corners still lift, lower the fan speed a step and retest. Keep enough fan for overhangs: Prusa notes that PLA and PETG need strong cooling, and that a low fan of 10 to 20% Starting point can help small features even in ABS or PC.
4. Stop drafts. Move the printer away from windows, fans and air conditioner vents. In a cold room, Bambu Lab suggests raising the bed about 10 °C Starting point, staying within the filament's range.
5. Add a brim. Prusa recommends a brim, and if that is not enough, a small easy-to-remove helper shape a few layers tall beside the problem corner. See Brims, Rafts and Skirts.
6. Keep heat around high-shrink materials. For ABS, ASA and PC, Prusa suggests an enclosure if you print them often, a draft shield (a tall skirt around the part) if you do not, grouping parts together and placing problem areas near the center of the bed. Do not enclose PLA or PETG this way: Prusa says they need strong cooling.
7. Reduce shrinkage in the model settings. Lower a high infill density and try a pattern such as gyroid, as Bambu Lab suggests for large parts.
8. Slow down for high-warp materials if the steps above are not enough.

Confirm it is fixed

Print the same part, or a long flat test bar with square corners, with the new settings. Check the corners after the first few centimeters of height, where lifting usually starts, and again at the end: a thin feeler such as a sheet of paper should not slide under any corner. Off the plate, the bottom should sit flat on a table without rocking.

Why it happens

Plastic leaves the nozzle hot and expanded and shrinks as it cools. Each new layer is laid on a layer that has already cooled and shrunk, so as the new layer shrinks it pulls inward on the layers below it. In the middle of a part those pulls cancel out. At a corner they all point the same way, inward and upward, so the corner is where the bond to the plate is tested hardest. Prusa explains that the bigger the gap between nozzle temperature and room temperature, the stronger this effect, which is why ABS, ASA and PC warp far more than PLA.

That is also why the fixes fall into two groups. Some make the bond stronger: the right bed temperature, a clean plate, a brim. Others reduce the pull: less cooling early, a warm and still room, an enclosure for high-temperature materials, less dense infill. A part that is held down hard but still shrinks fast can crack between layers instead of lifting, which is why Prusa warns that too much fan weakens layer bonding.

Warping is not only cosmetic. Prusa notes that it leaves stress locked inside the part, so reducing it also makes parts stronger. If layers are splitting apart higher up rather than lifting at the bottom, see Poor Layer Adhesion.