Ironing and Flat-Top Finishes: Mastering the Final Layer of FDM Parts
On many FDM prints, the sides look great but the top surface shows gaps, ridges and a "pillowed" texture. Ironing is a slicer feature that cleans up the last layer by running the nozzle across the already-printed top face with a small amount of extra extrusion, melting it flat. When tuned, it turns a rough top into a near-injection-molded surface.
What ironing actually does
After the final layer is deposited, the printer moves back over the flat top region without adding much new material — just a light re-melt of the existing surface. The nozzle largely seals voids and flattens the extrusion lines. The result is a cleaner, denser top that photographs and feels better.
Ironing settings to try
| Setting | Typical value | Effect |
|---|---|---|
| Ironing speed | 20–40 mm/s | Slower = smoother but slower prints |
| Ironing flow | 8–15% | Higher fills gaps, too high causes buildup |
| Ironing line spacing | 0.1–0.2 mm | Tighter spacing blends better |
| Ironing pattern | Concentric or Zigzag | Concentric often looks best on flat tops |
Not every slicer exposes all of these; start with flow around 10% and adjust one variable at a time. Ironing only helps flat top faces — it cannot fix a part that is already under-extruded or has visible layer issues underneath.
Workflow tips for a perfect top
- Use 3 or more top layers so the surface is dense before ironing.
- Increase top layer flow slightly if you still see gaps.
- Enable ironing only on flat regions to save time on curved parts.
- Match your hotend temperature to the filament — too hot and ironing leaves a glazed sheen.
Filament matters for the finish
The final texture also depends on the material. Matte filaments hide flaws but can absorb ironing differently, while silk filaments give a glossy, striking finish. For the most consistent flat-top results, use filament with a stable diameter. ANTINSKY PLA+ 1.75mm prints crisp details at 190–220 °C with a vacuum-sealed spool, PETG for durable functional parts, and ABS or TPU when the application calls for stiffness or flexibility. Small tweaks on the top layer, plus reliable material, are all it takes to make flat surfaces look finished.