Layers separating or cracking (delamination): causes and checks

How to recognise it

In delamination, two layers that should be fused together come apart: a sharp horizontal crack appears along the wall, often on tall or large parts, sometimes only when the part cools down or is bent. Prusa describes the cracks as clean cuts with the edge bent slightly upwards. It is a different defect from missing layers, where no material was deposited, and from shifted layers, where the model “steps” along X or Y.

According to Prusa, it happens because layers cool at different rates and the resulting shrinkage forces exceed the adhesion between one layer and the next. That is why the defect is more common with materials that shrink a lot, such as ABS and ASA, and on large parts, where temperature differences are greater.

The most common causes

Temperature too low: the new layer does not heat the one below enough and the two do not fuse. Prusa names a profile, official or custom, with wrong temperatures as the main cause; Creality also lists a temperature that is too low among the main causes of cracks between layers.

Too much cooling: part cooling fan set too high or cold ambient air. Prusa warns that with some materials more cooling can cause warping or layer separation and that ABS is very sensitive to cold air; Bambu Lab considers an enclosed printer with a heated chamber essential for ABS, ASA, PA and PC.

Too little material and layers too tall: with insufficient flow, layers have less contact area. Creality advises keeping the layer height below 80% of the nozzle diameter (about 0.32 mm with a 0.4 mm nozzle) and notes that very thin walls and high speeds encourage cracks. A partially clogged nozzle or wet filament can have the same effect: see the dedicated guides.

Checks to do, in order

Change one setting at a time and, after each change, reprint the same part or a tall, thin test piece.

1. Check that the material profile, printer profile and nozzle diameter in the slicer match the loaded filament and the installed nozzle.
2. Increase the nozzle temperature in 5 °C steps, staying within the filament manufacturer's range: for PLA, Prusa gives roughly 195–220 °C depending on the brand.
3. With ABS, ASA and other engineering materials, reduce the part cooling fan (for ABS, Prusa recommends switching it off completely), close the door and lid and keep the printer away from windows, air conditioners and fans.
4. Check the layer height: keep it below about 80% of the nozzle diameter.
5. If you print very fast, reduce the wall speed and increase the number of perimeters: thicker walls resist cracking better.
6. Calibrate the flow: Prusa suggests increasing the extrusion multiplier in 5% steps, checking with a calibration that you do not tip into over-extrusion.
7. If the defect remains, try another spool and check that the nozzle is not partially clogged.

Notes from manufacturer documentation

Prusa (PrusaSlicer): the extrusion multiplier is in the filament settings and is only visible in Advanced or Expert mode. For large parts, Prusa suggests considering PETG instead of ABS; ASA is an alternative but depends even more on a stable printing environment. Its cooling page notes that the “Keep fan always on” option is normally disabled for ABS, ASA, PC and some flexible materials.

Bambu Lab: for ABS, ASA, PA and PC it recommends an enclosed printer with a heated chamber; on open printers such as the A1 it advises raising the bed temperature by a further 10 °C against warping. Creality: besides temperature and layer height, it advises reducing speed and avoiding walls that are too thin, noting that a 0.4 mm wall cracks more easily than a 1.2 mm one.

What users report in the forums

In a thread on the Bambu Lab forum, a user with a P1S saw layers peeling apart when printing PLA with the Bambu Basic PLA profile at 220 °C; a temperature tower also separated. Another user, who called this kind of delamination typical of a temperature that is too low, suggested checking the filament profile first and then the thermistor; after the hotend was reinstalled with no improvement, they concluded the spool was defective. The thread reports no confirmed fix: it is one person's experience, but it shows why it is worth trying another spool before taking the hotend apart.

When replacing a part is justified

Usually there is no need: temperature, cooling, profile and flow solve most cases. An enclosed printer, or an enclosure for an open printer, is justified if you often print ABS, ASA or other engineering materials: both Prusa and Bambu Lab recommend it. Replace the nozzle or thermistor only if a check points to a clog or an unstable temperature.

How to verify the result

Record the model and variant, material, slicer profile and change made. Repeat the same test and compare the result with a photo taken before the adjustment. Keep the change only if it improves the defect without introducing others. Use your model’s instructions for temperatures, calibration and disassembly; this guide is not based on our own hands-on tests.