Ironing: Getting Flat, Glossy Top Surfaces

Logan F.

Smooth as Glass

The top surface of a standard FDM print consists of closely spaced parallel extrusion tracks, each slightly rounded on top. Under direct light, the ridges between tracks catch the light and make the surface texture highly visible, even when the layers themselves are well calibrated. Ironing addresses this issue by running the nozzle over the top surface again after printing it, with very low (or zero) extrusion, pressing and remelting the surface slightly to flatten the ridges. The result is dramatically smoother, often approaching the appearance of an injection moulded surface for flat, horizontal top faces.

Ironing adds a small amount of time to prints (typically 3–15% depending on the top surface area relative to overall print volume) and works best on horizontal flat surfaces, as it's less effective on sloped or highly curved top surfaces. But for prints where the top surface is a prominent design feature, it's one of the most impactful settings you can enable.

Enabling and Configuring Ironing

In Cura, search for “Ironing” in the settings menu. Enable “Enable Ironing” and configure the pattern, either Zigzag or Concentric, along with the flow rate, line spacing, and speed.

In PrusaSlicer, head to the “Infill” settings, enable “Ironing,” and adjust the same parameters there.

A good starting point is the following:

• Ironing speed: 15–25 mm/s
• Line spacing: 0.1–0.15 mm
• Flow rate: 10–20%

The slower speed gives the nozzle enough time to heat and smooth the surface properly. The fine line spacing helps achieve full surface coverage, while the low flow rate adds only a tiny amount of material to fill small gaps without increasing the part height.

The flow rate is the most important setting to dial in correctly. If it is too high, usually above 20–25%, ironing can create a visible extra layer on top of the print, making the surface look uneven or slightly raised. If it is too low, below around 5%, there will not be enough material to fill the small valleys between extrusion lines.

The goal is to apply just enough material to smooth out surface imperfections without adding noticeable thickness. The best way to tune this is by printing several small flat test tiles with different ironing flow rates and comparing them under angled lighting to see which produces the smoothest finish.

Materials and Limitations

PLA and PLA+ respond especially well to ironing because their lower printing temperatures make the heat during the ironing pass easier to control. PETG can also produce excellent results, although the extra heat may cause it to grip the bed surface more aggressively. When ironing PETG for the first time, keep an eye on bed adhesion throughout the print. ABS can be ironed as well, but the improvement is usually less noticeable due to the material’s naturally rougher and more moisture sensitive surface finish.

Ironing only affects flat, upward facing horizontal surfaces. It will not improve bottom layers, vertical walls, or downward facing overhangs. If you want a smoother finish across the entire print, combine ironing on the top surfaces with sanding and painting techniques from our finishing guide for the walls and underside. Another great option is printing with matte PLA, which naturally hides layer lines on vertical surfaces while ironing cleans up the top layers. Together, this combination can produce display quality results with very little post processing required.