What is Ironing in 3D printing?

The top surface of FDM prints can sometimes show lines or small grooves. Ironing is a slicer feature that makes the top layer extra smooth. After printing the top layer, the nozzle passes over the surface once more with a very small flow of material.

This fills in micro-gaps, flattens ridges, and gives you a cleaner finish. It’s useful for parts that will be visible (lids, housings) and components that need to look perfectly flat.

What exactly is ironing?

Ironing is an extra, slow pass over the top layer added by your slicer. The nozzle stays hot and moves in tight paths over the freshly printed surface. With a minimal flow, it presses a bit more material into the pores of the print.

The result is a smoother, more even top layer. Note: ironing only works on top surfaces (so not on walls or undersides).

How does it work in practice?

You enable ironing in your slicer. It then happens automatically on the highest top layer or, if you choose, on all top surfaces. The nozzle moves over these areas slower than usual, with a low flow and small line spacing to neatly "seal" everything. This adds extra print time, but it also saves you from having to sand or fill the part later.

When to use it (and when not to)

Ironing is ideal if the top will be visible or if you need a functionally flat surface. Think of lids, faceplates, front panels, or nameplates. Large, flat surfaces benefit the most.

There are also times when you shouldn't use it. On small top islands or fine details, the nozzle makes many start/stop movements, which can actually cause streaks or smudges. The effect is also limited on highly curved or organic surfaces. Skip it when print speed is more important than looks.

In short:

• Do use it if aesthetics or flatness matter and you have a reasonably large, flat top surface (PLA and PETG usually work very well).
• Don't use it for tiny top surfaces, relief/text that needs to stay sharp, highly curved shapes, or tight deadlines.

Still in doubt? Ask for no-obligation advice and we’ll let you know what the best choice is for your part.

The settings that matter most

There are several options, but these four determine a good 80% of your final ironing result:

• Range: Topmost only (only the very top layer) or All top surfaces. Topmost only is usually the best balance between time and results.
• Flow: start around 8–10% of your normal flow. Too high causes smearing/blobs; too low leaves pores visible.
• Speed: 15–30 mm/s often works well. Slower = smoother, but takes more time.
• Line spacing/pattern: choose a small spacing (a fraction of your nozzle diameter). A monotonic or rectilinear order provides a tighter "sheen."

Simple starting recipe: Topmost only, flow 8–10%, speed 20–25 mm/s, line spacing ±0.1–0.2× nozzle width. Print a small test plate afterwards and fine-tune.

What should you look out for? (material, model, and machine)

Regarding material behavior:

• PLA is forgiving and provides a nice satin finish.
• PETG can "smear" if you iron too hot or too slowly; lower the temperature or flow a touch.
• ASA/ABS react more quickly to heat: ironing too hot can cause edges to curl; better to go a bit cooler and not too slow.
• Nylon/PA must be dry, otherwise you will see micro-pitting.

Design details

Do you have relief or text on the top layer? Ironing can soften sharp edges just a bit. If you want to keep them crisp, turn off ironing for those areas or print the visible side on the build plate for a mirror-smooth finish (especially with a smooth sheet).

Machine and environment

• Keep your nozzle and cooling fans clean and consistent. A dirty nozzle is more likely to cause streaks.
• Iron at the same or a slightly lower temperature than your top layer. Too hot + too slow = risk of shiny spots or streaks.
• Make sure you have enough top layers before ironing (e.g., 5+). Ironing flattens the surface, but it won't fix a lack of top infill.

Common issues (and quick fixes)

Streaks or smudges after ironing.
Lower the flow in increments of 2–3% and/or iron a bit slower. Check that your nozzle is clean and that you have enough top layers before ironing.

Visible pores.
A touch more flow or a smaller line spacing helps. Also, check your top infill coverage (too sparse? fix that first).

Matte/glossy spots.
Experiment with a 5–10 °C lower ironing temperature or adjust the ironing pattern for an even sheen.

In summary

Ironing is an extra smoothing pass for your top layer. Use it wisely for visible parts and flat surfaces; skip it for small top areas, relief, or tight deadlines. With four core settings—range, flow, speed, and line spacing—you control 80% of the result.

Ready to get started? Run a quick test and note your winning settings for each material. Need to outsource? Upload your file directly or request no-obligation advice .