First-layer adhesion: a deep dive

The decision tree

When a first layer fails, the right order to check is roughly:

1. Bed cleanliness (~40% of failures)
2. Z-offset (~25%)
3. Bed temperature (~15%)
4. First-layer flow & speed (~10%)
5. Build plate condition (~5%)
6. Everything else (~5%)

Most “the bed leveling is broken!” posts on Reddit are actually number one. Most “this filament is garbage!” posts are number three.

1. Cleanliness

Skin oil is invisible and devastating. The fingerprint you left moving the plate twenty minutes ago is still there. The right cadence is:

• Wash the plate in warm water with dish soap, once per week of use.
• Wipe with isopropyl alcohol (≥90%) between every print session.
• Never wipe a hot plate; the oils smear instead of evaporating.

2. Z-offset

The “paper test” works once, then drifts. Run the Klipper or PrusaSlicer first-layer calibration print at the start of every long session. The goal is not “as low as possible” — it’s “extruded filament fully wets the plate without visible squish ridges between adjacent lines.”

3. Bed temperature

Cold bed is the second-most-common cause of warping. Hotter is not better past the filament’s recommended range — too hot and PETG glues itself to PEI permanently, eventually delaminating a layer of coating.

4. Flow & speed

A first-layer that prints at 100% speed is gambling. The right first layer is 30–40% slower than the rest of the print and 105–115% flow. This is conservative and it works.

5. Build plate condition

Textured PEI lasts ~6 months of heavy use; smooth PEI lasts ~12. Worn PEI looks fine to the eye and fails subtly. If you’ve been printing on the same plate for over a year and adhesion is flaky, replace the plate before chasing anything else.

What the printer can’t fix

A part with a 5 mm² footprint and a 200 g body will lift, no matter what you do. The fix is brim, not better adhesion.