Because the plastic shrinks as it cools, and the corners pull away where the first layer does not grip the bed well enough. Cleaning the plate, levelling again, checking the first-layer height and bed temperature, and keeping drafts off the printer usually solve it.
Lifting corners, often called warping, is one of the most common first-layer problems, and it has a short list of causes.
Why corners lift
Molten plastic contracts as it cools. The first layers cool while the upper layers are still being printed warm, and the pull concentrates at sharp corners, which are the points with the least adhesion around them.
Checks for lifting corners, in order
A clean plate. Fingerprints and dust stop plastic sticking; the plate maker’s cleaning advice applies to its surface. Levelling and first-layer height. A first layer that is too high rests on the plate instead of pressing into it. Bed temperature, within the range the filament maker publishes. Drafts. A window, a fan or air conditioning cools one side faster. The surface, since each plate type suits some filaments better than others.
Slicer settings that help
A brim adds grip around the edges. A slower first layer gives the plastic time to bond. Reducing part-cooling fan speed for the first layers helps on some materials.
When the material is the cause
ABS, ASA and some engineering filaments shrink more and need a warm, still space, which is why enclosures are recommended for them. Moisture in the filament can also weaken the first layer; drying the spool is worth trying when a material that used to print well starts to lift.
Questions makers ask before buying
Why does ABS lift more than PLA?
ABS and ASA shrink more as they cool and need a warm, still space around the print. An enclosure is the usual answer for them, while PLA rarely needs one.
Does a brim help?
Yes. A brim adds a thin extra area around the first layer that holds the corners down, and it trims off easily afterwards.
Last reviewed 15 September 2026