How to Fix Holes and Pillowing on the Top Surface

If the sides of the part are smooth but the very top surface comes out with holes, roughness or pillow-like bumps, the top layers have not covered the infill. This problem is called pillowing. The top layers are printed bridging over the sparse infill below. If the bridge is not thick enough, or the plastic does not cool well, it sags. The fix is usually in a few slicer settings.

Symptoms

• Small holes or gaps between lines in the top surface.
• The infill pattern showing through the top surface.
• Pillow-like bumps and rough textures on the surface.
• The problem is especially noticeable on flat, wide top surfaces.

What causes it?

Sparse infill leaves hollow pockets under the top surface. When the first top layer crosses these pockets, it prints lines hanging in the air. If these lines sag or curl, later layers cannot fully hide the defect. With enough top layers, each layer covers the flaws of the previous one a bit more, and a flat surface forms at the top.

1. Increase the top layer count

The most effective fix. In the slicer, increase the number of top layers or the top shell thickness.

• Total top shell thickness should be at least 0.8–1.0 mm.
• At 0.2 mm layer height, that means 4–5 top layers.
• At 0.12 mm layer height you need 7–8 top layers.

Some slicers ask for thickness and not layer count. If both thickness and layer count are controlled, the slicer applies the larger one.

2. Check the infill percentage

A very low infill percentage (5–10%) forces the top layers to bridge over very long distances.

• If top surface quality matters, raise infill to 15–20%.
• Patterns like gyroid and cubic can support the top layers better than grid.
• Some slicers have a setting that makes only the few layers under the top surface denser (for example "Gradual Infill" in Cura). That way the top surface is supported without increasing total material.

For details: Infill settings.

3. Increase cooling

Because the top layers are printed like a bridge, they need to cool fast.

• PLA: Use the part cooling fan at 100% on the top layers.
• PETG: Raising the fan to 50–70% improves the top surface.
• ABS/ASA: Raising the fan a lot causes layer cracking. Try raising it to around 20–40% on the top layers only.

Check that the fan really works and that the air duct blows toward the nozzle tip. A broken or badly fitted fan duct puts all the cooling on one side.

4. Fix under-extrusion

If not enough plastic is printed, the top layers are left with gaps. If you see thin lines and gaps over the whole part, solve the under-extrusion problem first. If there is a slight shortfall, do a flow rate calibration.

5. Lower the top layer speed

Top layers printed fast do not get enough time to cool.

• Lower the top surface speed to 30–60 mm/s.
• Keep the top surface line width close to the nozzle diameter.

6. Use ironing

Ironing is when, after the top layer, the slicer passes the nozzle over the surface once more while extruding very little plastic. The hot nozzle smooths the surface and closes small holes.

• Gives very good results on flat top surfaces.
• Lengthens the print time.
• Does not help on curved surfaces.

7. Top surface pattern

For the top surface, the monotonic (one-direction) pattern gives a more even look because it prints the lines always in the same order. The concentric pattern is preferred on some round surfaces.

Settings table

There are holes on the bottom surface too. Is the fix the same?

Holes on the bottom surface are usually a first layer problem. Look at the first layer and Z offset settings. Also check the bottom layer count.

Does increasing the top layer count too much do harm?

Material and time go up, but quality does not suffer. Going above 8–10 layers usually gives no extra benefit.