First Layer Won't Stick

Likely causes, most common first

1. Nozzle too high (Z offset or live adjust)Most common
   If the gap is too large, the lines are not pressed into the plate. UltiMaker describes exactly this: the lines are not pressed into the build plate, and the print can come loose during printing.
2. Dirty plate: skin oils, grease, residueVery common
   Touching the print surface leaves oils that stop plastic bonding. Prusa says you need to clean the sheet when it has been touched by hands or dirty tools.
3. Bed not level, or the mesh not runCommon
   A bed that is closer at one corner than another gives a good first layer in one place and a loose one elsewhere. On printers with automatic mesh leveling, a skipped or stale mesh does the same.
4. Wrong surface or adhesive for the materialCommon
   Different filaments stick best to different sheets. Prusa notes that a glue stick helps materials like PETG, ABS and ASA but is not needed for PLA on its sheets.
5. Bed temperature too low for the materialOccasional
   Use the bed range printed on the filament box or its data sheet. Prusa suggests raising the bed 5 to 10 °C for materials that do not stick well Starting point.
6. First layer printed too fastOccasional
   A fast first layer has less time to bond. Prusa's fallback is to slow the first three layers to about 75 percent Starting point.
7. Cooling fan on during the first layersOccasional
   Prusa notes that cooling the first layer is usually not necessary, and that skipping the fan for a few early layers (typically 1 to 5) helps prevent warping and detaching Starting point.
8. Drafts across the printerOccasional
   An air conditioner, open window or room fan cools the first layers the same way the part fan does, usually on one side. If lifting is always on one side of the plate, suspect airflow.
9. Warped, damaged or worn plateLess common
   Prusa lists a sheet that is not seated flat, is damaged or still has old filament on it as a cause. A sheet that never recovers after a thorough clean may be worn out.

Fix it, one change at a time

1. Clear the plate and check it is seated. Remove leftover plastic, make sure the sheet sits flat and nothing is trapped under it.
2. Clean it properly. Prusa recommends 90% isopropyl alcohol Maker spec on its sheets and warns against low-percentage or cosmetic alcohols, which can contain oils. If adhesion still fades, wash the sheet with dish soap and warm (not hot) water, rinse, and dry it fully. Follow your plate maker's instructions: some coatings must not see acetone or certain cleaners. From now on, handle the sheet by its edges.
3. Re-run leveling or the bed mesh with the bed and nozzle at printing temperature if your printer supports it.
4. Set the nozzle height while watching a first-layer test. Use your printer's Z offset, live adjust Z or first-layer calibration and lower the nozzle in small steps until the lines are flat and touching. Prusa advises against lowering it further just to make a poorly cleaned plate stick.
5. Match the surface and bed temperature to the material. Use the bed range on the filament label and the right sheet or adhesive for that filament. Raise the bed a few degrees within that range if needed.
6. Slow the first layer and keep the fan off for the first few layers. Check the slicer's first-layer speed and the setting that disables the part fan for the first layers.
7. Add a brim for small contact areas, sharp corners or tall narrow parts. Prusa suggests trying a brim before reaching for extra adhesives.
8. Shield the printer from drafts if lifting always happens on one side.
9. Replace the sheet if a clean, correctly leveled plate at the right height and temperature still will not hold.

Confirm it is fixed

Print a single-layer test patch, or the first few layers of the real job. The lines should be flat, joined into a continuous sheet with no gaps, and should not lift when you run a fingernail along an edge. Then print the full part and check the corners after the first few centimeters, where lifting usually starts.

Why it happens

The first layer is the only layer that bonds to something other than plastic. For it to hold, three things have to happen at once: the melted line has to be pressed onto the surface with the right gap, the surface has to be clean enough for the plastic to wet it, and the line has to stay warm long enough to bond before it shrinks.

Nozzle height controls the pressing. Too high and the line is laid on top of the plate like a thread on a table; it can be pulled off by the next move or by the part shrinking as it cools. Too low and there is no room for the plastic to flow, which gives a thin, rough layer and can scrape the plate.

Cleanliness controls wetting. A fingerprint is a thin film of oil, and the hot plastic bonds to the oil film instead of the plate. That is why a plate that worked yesterday can fail today after one touch, and why Prusa recommends washing with dish soap when alcohol alone stops working: soap and water remove residues that alcohol leaves behind.

Temperature and cooling control the bonding time. Plastic shrinks as it cools, and that pulls the edges and corners of a part inward and upward. A warm bed, a slower first layer and no fan for the first few layers all keep the first layer soft for longer. Drafts work against all three, usually on one side.

Getting the first layer right also matters for everything above it: thick or uneven first layers spoil fine detail. See Choosing a Layer Height for how the first layer height relates to the rest.