Layers separate or the part cracks between layers

Symptom

The part opens up in horizontal cracks or splits cleanly along a layer, often with the edges bowed upwards. It is more common with ABS and ASA and on large parts.

Likely causes, from most to least likely

1. Nozzle temperature too low for that filament: the layers don't fuse properly.
2. Uneven cooling: part cooling fan too high, draughts or no enclosure with materials such as ABS or ASA. Shrinkage pulls the layers apart.
3. Under-extrusion or speed beyond what the hotend can melt: poor bonding between layers.
4. Wet filament, which reduces layer adhesion.

Checks to tell which one it is

• Compare the temperature with the filament manufacturer's range; as a reference, Prusa says PLA prints between 195 and 220 °C depending on the brand.
• Check the part cooling fan speed in the profile and whether there are windows, doors or air conditioning nearby.
• Look for other signs of under-extrusion (thin lines, gaps) or moisture (bubbles, strings).

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

1. Raise the nozzle temperature

   Increase the temperature in 5 °C steps (Prusa's guideline), staying within the filament manufacturer's range, until the layers bond well.

   Check: Layers are well bonded and the part doesn't split.

   If that does not fix it: Reduce cooling and draughts.

2. Reduce cooling and draughts

   With ABS, turn the part cooling fan off (Prusa recommends it); with ASA or PC, keep it to a minimum. Move the printer away from windows and air conditioning.

   Check: No new cracks appear.

   If that does not fix it: Print technical materials enclosed.

3. Print engineering materials enclosed

   For ABS, ASA or PC, use an enclosed printer or an enclosure that keeps the air warm and draught-free.

   Check: Large parts finish without cracks.

   If that does not fix it: Fix under-extrusion.

4. Fix under-extrusion

   Lower the speed or maximum volumetric flow. If material is missing, raise the extrusion multiplier; Prusa suggests 5% steps to strengthen layer bonding, watching that over-extrusion doesn't appear.

   Check: Layers look continuous and well bonded.

   If that does not fix it: Dry the filament.

5. Dry the filament

   If you see bubbles or a lot of stringing, dry the spool at the temperature and for the time its manufacturer gives before continuing.

   Check: Layer bonding improves with dry filament.

   If that does not fix it: Change material if needed.

6. Change material if needed

   For large parts, Prusa suggests PETG or ASA as alternatives to ABS: PETG is the least prone to cracking and ASA depends more on a stable environment.

   Check: The part comes out without cracks in the new material.

   If that does not fix it: Ask the filament manufacturer for its recommended printing conditions.

Prevention

• Print ABS and ASA enclosed and away from draughts.
• Use the filament manufacturer's temperature range and fine-tune it for each spool.
• Keep filament dry.

Still not fixed?

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Printers it applies to

Any FDM (filament) 3D printer, from any brand.

Official sources

This guide summarises the official documentation linked here:

• Layer separation and splitting FDM · Prusa Research
• Cooling · Prusa Research
• Max volumetric speed · Prusa Research
• Drying filament · Prusa Research