Layer separation (delamination) — 6 causes of cracking along the layers

Symptom: the finished print falls apart along the layer lines. Sometimes the gap is already visible on the machine, sometimes the model looks fine but cracks when you first tighten a screw or try to bend it. The fracture is flat and runs exactly in the XY plane, not diagonally through the material.

Layer separation, or delamination, is the absence of a weld between neighbouring layers. In FDM printing every new path has to melt into the one laid before it so that the polymer chains have time to entangle with each other. If the previous layer is already too cold, or the fresh material carries too little energy, you get a mechanical contact instead of a weld. The print holds its shape, but on the Z axis it has a fraction of the strength it has in the plane of the bed. The problem affects above all materials with a high processing temperature, that is ABS, ASA, PC/ABS, PA and HT PETG.

Most common causes and fixes

1. The nozzle temperature is too low for the material and for the speed

This is the first thing to check. The range given by the manufacturer assumes a moderate speed. When you print fast, the polymer spends less time in the heater block and comes out cooler than the thermistor indicates. The bottom of the range, which was enough at 40 mm/s, at 120 mm/s already gives layers that do not bond.

How to check: print a temperature tower and break each segment with your fingers. Segments from the lower part of the range will snap cleanly and without resistance; the upper ones will tear with visible stretching of the material.

What to do: raise the nozzle temperature in 5 °C steps towards the upper limit of the range for the material in question. With ABS and ASA aim for the upper half of the range if you care about the strength of the part rather than about detail. Do not go above the manufacturer's range, because you will start degrading the polymer and collect burn marks.

2. Cooling is too aggressive for the polymer in question

The part cooling fan is PLA's friend and ABS's enemy. The airflow takes away from the layer exactly the heat that was meant to melt into the layer below. Porima gives a different fan range for each material and that is not a cosmetic suggestion but a condition for getting a weld.

How to check: look at where the print delaminates. If the gaps are only on one side of the model, the side the fan blows at, the cause is obvious.

What to do: set the fan according to the range for the material. For ABS that is 0–40 %, for ASA and PC/ABS 0–30 %, for HT PETG practically zero, because the range ends at 10 %. Nylon is the exception: the first five layers are printed with the fan off, and only then can it be opened up.

Porima material	Nozzle	Fan	Chamber
PLA	200–230 °C	100 %	open
PETG	240–260 °C	100 %	open
HT PETG	270–300 °C	0–10 %	enclosed recommended
ABS	250–280 °C	0–40 %	enclosed, 50 °C
ABS/CF	260–280 °C	0–40 %	enclosed, 50 °C
ASA	250–280 °C	0–30 %	enclosed, 50 °C
PC/ABS	260–290 °C	0–30 %	enclosed, 50 °C
PA (nylon)	260–290 °C	30–100 %, first 5 layers without	enclosed, heated
TPU Flex 98A	230–260 °C	40–70 %	open

Source: the official FDM technical data table from the manufacturer, Porima. All materials: print temperature table.

3. No chamber, a draught, or an open window in the workshop

Even with the fan switched off, a layer cools from its surroundings. A printer standing by a tilted-open window, or in a garage in winter, cools the print just as effectively as active part cooling, only unevenly: the lower sections cool faster than the upper ones, so the gap appears at a random height. For ABS, ASA, PC/ABS and ABS/CF, Porima explicitly specifies an enclosed chamber at 50 °C, and for nylon an enclosed and heated chamber.

What to do: enclose the printer. It does not have to be a factory enclosure; a box made of board or a tent of foil is enough, as long as it holds temperature steadily and keeps draughts out. Always provide extraction for the fumes, especially with ABS and ASA. If you do not have a chamber and are not going to have one, choose a material suited to the conditions: PETG prints in an open machine without trouble and has a declared temperature resistance of 85 °C.

4. The layer height is too large relative to the nozzle

The thicker the layer, the smaller the ratio of contact area to path cross-section and the weaker the weld. With a 0.4 mm nozzle a 0.32 mm layer is already the limit of good sense, and a 0.35 mm layer is a direct route to delamination with technical materials.

What to do: adopt the rule that layer height does not exceed about three quarters of the nozzle diameter. If you need thicker layers to save time, fit a 0.6 mm nozzle rather than raising the layer height on a 0.4. Remember at the same time that PLA Wood and PLA Star require a 0.6 mm nozzle by design, and PLA Premium in the Granite version also works with 0.6.

It also helps to raise the extrusion multiplier by a few per cent and to increase the path width. A thicker path means a larger contact area and a greater reserve of heat.

5. The filament has absorbed moisture

Water flashes to steam in the nozzle and creates microbubbles in the strand. Where there is a bubble there is no weld, there is a void. A print made from wet nylon can have Z-axis strength lower by an order of magnitude and cracks along the layers under ordinary handling. Nylon is the extreme case here: Porima describes its moisture resistance as low and drying as mandatory.

How to check: listen to the nozzle during a dry extrusion. Crackling, hissing and steam are an unambiguous symptom. The second clue is a matte, porous surface where the material should be smooth.

What to do: dry the spool before printing, and print technical materials straight from the dryer.

Material	Temperature	Time
PLA and PLA variants	30–40 °C	2–4 h
PETG	30–40 °C	2–4 h
HT PETG	50–60 °C	6–12 h
ABS / ASA / PC/ABS	40–60 °C	6–12 h
PA (nylon)	65–80 °C	8–12 h — mandatory
PLA/CF	55 °C	4 h
TPU Flex 98A	40–60 °C	2–4 h

Full guide: filament drying — temperature and time for every material.

6. Print speed exceeds what the hotend can deliver

High speed shortens the contact time between the hot path and the layer underneath and at the same time lowers the real temperature of the polymer. The effect compounds with cooling. If you raised the speed after changing printer or profile, and the delamination appeared along with that change, you have your answer.

What to do: drop the speed by a quarter and print the same model. If the weld comes back, choose one of two options: stay at the lower speed, or raise the nozzle temperature enough to compensate for the shorter time in the heater block. With TPU there is no choice, that material is printed slowly by design.

Which material is most at risk

The ranking is predictable and follows from the processing temperature. The hardest are ABS, ABS/CF, ASA and PC/ABS, because they have high shrinkage and require a chamber. Right behind them is nylon, which adds extreme water absorption to a high temperature. HT PETG delaminates less often, but requires a bed at 100–120 °C and a fan that is practically switched off. At the opposite pole stands the PLA family, which with full cooling and an open printer gives strong layers with no special measures at all.

If a part is to carry load on the Z axis, it is worth considering a change of orientation on the bed rather than fighting the settings. Rotating the model by 90° often moves the stress from the plane where the layers are bonded to the cross-section of the path, where the polymer is several times stronger.

Related problems

• Warping — the same mechanism of shrinkage and cooling, only the symptom appears at the bed rather than halfway up.
• Wet filament — crackling in the nozzle and a porous surface, a common hidden cause of weak layers.
• Under-extrusion — too little material in the path means too little weld area.
• Weak infill — infill that does not join the walls lowers strength just as delamination does.
• Dimensional accuracy and shrinkage — shrinkage stresses tear the layers apart from within.
• Smell and fumes — an enclosed chamber solves ABS delamination, but calls for well-thought-out ventilation.
• Brittle filament — over-dried or long-stored material gives a weak weld despite correct settings.