How to Stop Warping and Curling Corners in PLA and PETG 3D Prints

Warping is when the corners or edges of a print lift away from the build plate during printing. It starts as a tiny gap at one corner, and by the end of a long print it can bend a flat base into a shallow curve — or pull the part off the bed completely.

PLA is famous for being easy, but large flat parts such as wall signs, shelves and trays can still warp, and PETG has its own adhesion quirks. This guide explains why warping happens and how to stop it.

Why prints warp

Plastic shrinks as it cools. Each new layer is laid down hot on top of layers that have already cooled and shrunk, so the upper layers pull inward as they cool. The forces add up, and the part tries to curl upward from its edges — especially at sharp corners, where the pulling forces concentrate.

If the bottom layer sticks to the bed more strongly than those forces, the part stays flat. If not, the corners lift. Everything that reduces shrinkage forces or improves adhesion helps.

Fix 1: A clean, well-prepared bed

Oils from fingertips are the most common cause of poor adhesion. Wash PEI and textured plates with warm water and dish soap, rinse and dry them; wiping with isopropyl alcohol between prints helps, but a proper wash removes far more. Avoid touching the print surface.

A correct first layer is equally important. The nozzle should press the first layer slightly into the plate so lines are flattened and touching. A first layer that is too high gives round, separated lines that peel off easily. Our first layer adhesion guide covers leveling and Z-offset in detail.

Fix 2: Bed and room temperature

A heated bed keeps the bottom layers warm and slightly soft, which reduces the stress that causes lifting. Drafts are the enemy: a window, fan or air conditioner blowing across the printer cools one side of the part faster than the other and causes corners to lift.

Typical bed temperatures and plates
Material	Bed temp	Good surfaces	Notes
PLA	55–65°C	Smooth or textured PEI	Keep drafts away; enclosure rarely needed
PETG	70–85°C	Textured PEI	Can bond too strongly to smooth PEI or glass — use a release agent
ABS / ASA	90–110°C	PEI with enclosure	Needs an enclosure to prevent warping

Fix 3: Brims, mouse ears and adhesives

A brim adds a thin, wide border around the first layer, increasing the area that holds the corners down. A 5–8 mm brim is usually enough. Mouse ears — small discs at the corners — do the same job with less clean-up. Many slicers can add brims only where needed.

Glue stick or a dedicated adhesion product can help PLA stick to smooth plates, and acts as a release layer for PETG on smooth PEI, preventing it from bonding so strongly that it tears the surface.

Cooling the first layers

Turn the part-cooling fan off for the first two or three layers so the base stays warm and bonds well, then ramp it up gradually. For PETG, keep fan speeds moderate throughout.

Fix 4: Design and slicing choices

Sharp 90° corners concentrate stress. Rounded corners (fillets) of even a few millimetres greatly reduce lifting on large flat parts. Very large solid bases can be hollowed or ribbed to reduce the amount of plastic shrinking at once.

Lower infill and fewer bottom layers reduce shrinkage forces slightly. For wide, flat models such as wall signs, printing slightly slower on the first layers and using a brim is often all that is needed.

Diagnosing where warping starts

Watch the first few layers of a large print closely. If a corner lifts during the first layer, the problem is adhesion — clean the plate and adjust the first layer height. If corners stay down at first but lift after many layers, shrinkage forces are winning — add a brim, block drafts and consider rounded corners.

Check whether the warping always happens on the same side of the bed. A consistent side often points to a draft from a window, door or air conditioner, or to a bed that is not heating evenly. Moving the printer or using a simple cover to block airflow can fix it immediately.

If warping appears only with one spool of filament, the filament may be wet or of a different blend. Drying it or switching brands is a quick way to test.

Removing a brim cleanly

A brim is only useful if it comes off neatly. Let the print cool, then peel the brim away from the part at a corner and work around it. Use a deburring tool or a sharp hobby knife to trim the small edge left behind. Setting a small brim-object gap in your slicer (around 0.1 mm) makes brims much easier to remove without marking the part.

Quick Checklist

Wash the plate with soap and water; avoid touching it
Get a slightly squished, even first layer
Set the right bed temperature and block drafts
Add a 5–8 mm brim or mouse ears to large flat parts
Use a release agent for PETG on smooth plates
Prefer rounded corners on large flat designs

Frequently Asked Questions

Does PLA need an enclosure?: Usually not. An enclosure can even cause PLA to soften and clog in some printers. Block strong drafts instead.
Why did my PETG print rip the bed surface?: PETG can bond extremely strongly to smooth PEI and glass. Use a textured plate or a thin layer of glue stick as a release agent.
Should I raise the bed temperature if corners lift?: A small increase can help, but too hot makes the base soft and can cause “elephant's foot”. Fix cleanliness and first layer height first.
Can warping happen in the middle of a print?: Yes. Tall parts can split between layers or lift later as stress builds up. Better layer adhesion, fewer drafts and rounded shapes help.

Warping is a contest between shrinkage and adhesion. Win it with a clean plate, a good first layer, steady temperatures, a brim where needed and rounded corners — and even large flat signs and trays will stay perfectly flat.