Over-extrusion in 3D printing — 5 causes and how to fix it

Symptom: the walls are bulging and rough, the corners swell, surplus beads of plastic appear on the surface, and the dimensions of the finished part come out larger than the model. Holes are tighter than they should be, and nothing will go into them without drilling.

Over-extrusion (too much material) is the mirror image of a shortage: more plastic passes through the nozzle than the slicer planned for. The excess has nowhere to go, so it pushes the line out sideways and upwards. The next layer is laid on an uneven base and the error grows with every layer. Dimensional accuracy suffers most, because the outer wall grows outwards into the space around the model while holes shrink inwards.

The most common causes and their fixes

1. The extrusion multiplier is simply too high

The Flow parameter (in Cura Flow, in PrusaSlicer Extrusion multiplier) multiplies the entire volume of plastic delivered. Values above a hundred per cent usually get into a profile during a fight with under-extrusion and stay there for ever, long after the original problem has gone.

How to check: print a cube with a single wall, no infill and no top layers, then measure the wall thickness with callipers at several points. It should match the extrusion width set in the slicer. Every tenth of a millimetre above that value is excess material.

What to do: change the multiplier by two per cent at a time and repeat the measurement each time. Do not set it by eye, set it by callipers. With high-gloss materials such as Silk PLA the eye is fooled particularly easily, because the light hides how convex the lines really are.

2. The filament diameter in the slicer does not match reality

Volume is calculated from the square of the radius, so a small error in the diameter field gives a disproportionately large error in flow. A profile with 1.75 mm entered, fed with filament that is really 1.79 mm, will deliver noticeably too much material even though the multiplier sits at a hundred per cent.

How to check: measure the filament with callipers at five points about a metre apart, always on two perpendicular axes, and work out the mean.

What to do: enter the measured mean into the profile before you touch the multiplier. Porima filaments are produced to a ±0.03 mm tolerance, so one good set of measurements will do for the whole spool. Filament with a wide spread of diameter, on the other hand, cannot be calibrated at all: on the same profile you will get too much one moment and too little the next.

3. The nozzle temperature is too high

Hotter plastic is thinner, flows out more easily by itself and stays soft for longer once laid down, so it flattens under the weight of the layers above. The symptom looks like excess material, even though the slicer is delivering exactly the right amount.

How to check: print a temperature tower. If along with the bulges you can see stringing, scorching or glossy runs at the corners, it is the temperature, not the flow.

What to do: come down in 5 °C steps towards the bottom of the range specified for the material. We have collected the limits in the table below. Below the lower value the layers will stop bonding, so that is the hard floor for this correction.

4. The bed is too hot or the first layer is pressed too hard

Over-extrusion is often reported by people whose problem affects only the bottom few millimetres of the model. That is usually not extrusion at all but too warm a bed, on which the lower layers stay soft and spread sideways, or too low a Z-axis offset.

How to check: measure the width of the part just above the bed and at half its height. A difference means elephant's foot, not a global excess of material.

What to do: bring the bed temperature down to the lower part of the range and correct the offset. You will find the bed ranges in the table too — PLA prints even on a cold bed, while ASA and HT PETG require high temperatures at which softening of the bottom layers is built into the material.

5. The line width does not match the nozzle

The slicer sets the extrusion width from the nozzle diameter entered in the printer profile. Fitting a larger nozzle without updating that field is instant over-extrusion: the profile calculates for 0.4 mm while the orifice delivers material like a 0.6 mm one.

What to do: check in the printer settings which nozzle diameter is entered there and compare it with what you actually have in the head. Remember that some Porima materials need a larger orifice by design: PLA Wood and PLA Star are printed with a 0.6 mm nozzle, as is the Granit variant in the PLA Premium line.

Porima material	Nozzle range	Bed range
PLA	200–230 °C	0–60 °C
Tough PLA (PLA+)	210–240 °C	0–60 °C
Hyper PLA+	220–250 °C	0–60 °C
Silk PLA	230–260 °C	0–60 °C
PLA Premium	210–240 °C	0–60 °C
PLA/CF	220–250 °C	50–70 °C
PETG	240–260 °C	60–80 °C
HT PETG	270–300 °C	100–120 °C
ABS	250–280 °C	80–110 °C
ASA	250–280 °C	90–120 °C
PA (nylon)	260–290 °C	90–120 °C
TPU Flex 98A	230–260 °C	40–60 °C

Source: the official FDM technical data table from the manufacturer, Porima. The complete set of 25 materials: print temperature table.

Quick checklist

Measure the filament with callipers and enter the real diameter into the profile.
Check that the nozzle diameter in the printer settings matches the one fitted.
Print a single-wall cube and measure the wall thickness.
Adjust the extrusion multiplier two per cent at a time, always with a measurement.
Lower the nozzle temperature by 5 °C and judge the difference.
Bring the bed temperature down if only the bottom layers are swelling.
Finally, check the dimensions of the holes, because that is where the error shows up first.

The overriding rule: change one parameter at a time. Calibration without callipers is guesswork.

Why this ruins dimensions more than you would think

Excess plastic is not distributed evenly. The outer outline grows outwards, so a peg comes out too thick and a hole too narrow. On a fit that means a double error: the part grows by the excess and the socket shrinks by the same excess. That is why prints with uncalibrated extrusion can fail to go together even though each looks fine on its own. The second consequence is less obvious: excess material collects on the edge of the nozzle and after a few dozen layers drops onto the model as a blob. If you see zits on the surface alongside bulging walls, treat it as one problem, not two.

It is also worth knowing when over-extrusion is deliberate. The first layer usually has its own, higher multiplier and is meant to, because the plastic has to spread out on the bed. In the same way, bridging lines are sometimes deliberately thinner. So check your calibration on the wall of the model, not on those sections.