Guide to Ironing: How to make top surfaces super smooth with PrusaSlicer 2.3 (RC)

The top surface of 3D prints is typically not perfectly smooth. As the nozzle draws the perimeters and solid infill, small gaps and ridges remain visible between the toolpath lines. However, if your model has flat areas parallel to the print bed, you can use Ironing to smooth them.

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How does ironing work?

Ironing smooths flat top surfaces by running a special second infill phase in the same layer.

As the hot nozzle travels over the just printed top layer, it flattens any plastic that might have curled up. The nozzle also extrudes a small amount of filament to fill in any holes in the top surface. The spacing between individual ironing passes is usually a fraction of the nozzle diameter. That means the nozzle will go over the same spot several times. Ironing is angled at fixed 45 degrees compared to the first phase of normal top infill as this approach produces better results.

Macro comparison of Ironing OFF (left), Ironing ON (right)

PrusaSlicer 2.3

At the time of the release of this article, PrusaSlicer 2.3 is available as a release candidate version. You can download it from our GitHub. You will not find ironing in the previous versions of PrusaSlicer.


The Ironing idea was first proposed in 2016 by the Spanish user “Neotko” on the Ultimaker community forum. Neotko prototyped “Neosanding” – a smoothing of top surfaces in Simplify3D by running a second infill phase at the same print height with zero or a tiny extrusion rate perpendicularly to the first infill run. The “Neosanding” was later integrated by Ultimaker into their Cura slicer. Kisslicer integrated Ironing with a small twist: The second phase is not perpendicular to the first phase, but at 45 degrees, which Jonathan, the author of Kisslicer, validated to produce better results. For PrusaSlicer, we implemented Neotko’s “Neosanding” at 45 degrees as in Kisslicer.

When to use Ironing

Ironing is useful for prints with flat top surfaces, like nameplates, logos, badges, boxes, lids, etc.

It can also be useful when you want to glue two pieces together and need the surfaces to be as flat as possible so that the gap between them is minimized.

Ironing is not useful for round objects, figures and organic shapes in general. It’s also not useful for objects which do have flat areas, but these flat areas are not aligned parallel to the print bed. With that said, ironing will not have a significant negative impact when printing such models. It will just unnecessarily increase the print time.

Guide to Ironing: How to make top surfaces super smooth with PrusaSlicer 2.3 (RC) - slope ironing on off

Ironing has little to no effect on non-flat surfaces, Ironing Off (left), Ironing On (right)

Don’t forget, that some models can be printed upside down. The bottom layer printed on the build plate will typically be even smoother than an ironed top layer (depending on the print sheet that you use).

Use in combination with the Monotonic infill

The Monotonic infill is another feature, which improves the quality of the top layers. It’s essentially the good old rectilinear infill with modified path planning – it’s always extruded only in one direction (e.g. left to right). Use it in combination with Ironing to get the best results. Original Prusa profiles have the Monotonic infill already

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