You’ve dialed in every other setting and the top surface still looks like corduroy. Visible extrusion lines, tiny gaps between passes, and a texture that screams “3D printed.” Ironing is the final surface finish pass that melts and smooths the top layer — but dialing it in wrong makes the surface worse than leaving it alone. Here’s exactly how to configure ironing for a glossy, professional top finish.
How Ironing Actually Works
Ironing is a second pass over the top surface after the final solid layer is complete. The nozzle moves back across the part without extruding new material — instead, it re-melts the existing top surface with the nozzle tip and extrudes a tiny amount of additional filament to fill the gaps between extrusion lines. The result: the individual lines merge into a continuous smooth surface.
The key variables that determine whether ironing improves your part or ruins it: flow rate, speed, nozzle spacing, and temperature. Get any one of them wrong and you’ll get over-extrusion blobs, under-extrusion streaks, or a surface that’s rougher than the un-ironed version.
Parameter Configuration
Ironing Flow Rate
Flow rate is the most critical setting. This is the percentage of normal flow that the extruder pushes during the ironing pass. Default values in most slicers are too conservative (10%).
Starting point: 8-12% for PLA, 10-15% for PETG, 5-8% for ABS. The goal is to fill the ~0.05mm gap between extrusion lines without adding visible ridges.
Too high: The nozzle pushes excess material that squishes sideways, creating raised ridges on the surface. At 20%+ with PLA, you’ll see a visible smear pattern. At 30%+, the nozzle will drag through the excess and create grooves.
Too low: Gaps between layer lines remain visible. The nozzle passes over without depositing enough material to fill them. At 5% or below, ironing does nothing — you’re just running a hot nozzle over cold plastic.
How to calibrate: Print a 30×30mm flat calibration square, 2mm tall. Iron only the top layer. Start at 10% flow, print squares at 8%, 10%, 12%, and 14%. The correct value produces a uniform matte-to-satin finish with no visible extrusion lines and no ridges. Under a bright light at an angle, the surface should be uniformly smooth.
Ironing Speed
Speed determines how long the nozzle dwells over any given area. Slower = more heat transferred into the surface = better line merging.
PLA: 15-25 mm/s. PLA melts easily and doesn’t need much dwell time.
PETG: 10-15 mm/s. PETG has higher melt viscosity and benefits from slower ironing.
ABS/ASA: 20-30 mm/s. ABS responds well to faster ironing because it softens at a lower contact temperature.
TPU: 10-15 mm/s, with reduced flow (5-8%) — TPU smears easily.
Too fast: The nozzle passes before the plastic has time to re-melt. Lines remain visible. At 40+ mm/s with PLA, ironing is cosmetic noise — you’re just scratching the surface.
Too slow: The nozzle dwells too long and overheats the local area. The surface develops a wavy, melted appearance. At 5 mm/s, you’re cooking the top layer, not smoothing it.
Ironing Line Spacing
This sets the distance between adjacent ironing passes. Standard extrusion line width is 0.4mm (for a 0.4mm nozzle), so the default ironing spacing is 0.1mm — the nozzle passes once every 0.1mm, overlapping significantly.
Recommended: 0.1-0.15mm for most materials and nozzle sizes. At 0.1mm, every point on the surface gets approximately 4 overlapping ironing passes. At 0.15mm, about 2.7 passes. You can go as low as 0.05mm for a mirror finish, but each halving of spacing doubles ironing time.
Real-world trade-off: On a 100×100mm top surface at 0.1mm spacing at 20mm/s, ironing takes ~5 minutes. At 0.05mm spacing, ~10 minutes. On a large flat part (200×200mm), ironing at 0.05mm can add 30+ minutes to print time. For functional parts, 0.1mm is the sweet spot — good finish with reasonable time.
Material-Specific Ironing Settings
| Material | Flow Rate | Speed (mm/s) | Spacing (mm) | Nozzle Temp | Notes |
|---|---|---|---|---|---|
| PLA | 8-12% | 20 | 0.1 | Normal print temp | Easiest to iron. Start at 10% and adjust. |
| PLA Silk | 5-8% | 25 | 0.15 | Normal temp | Silk PLA smears easily — lower flow. The glossy additives melt differently. |
| PETG | 10-15% | 15 | 0.1 | Normal temp | Higher viscosity needs slower speed. Strings on travel moves are a risk — enable “Iron Only Highest Layer.” |
| ABS/ASA | 5-8% | 25 | 0.1 | Normal temp | Warping during the ironing pass is unlikely but possible on very thin parts. |
| TPU | 4-6% | 15 | 0.15 | 5°C below normal | Flexible filaments drag. Low flow, higher spacing. Expect a matte finish, not gloss. |
| Nylon | 6-10% | 20 | 0.1 | Normal print temp | Nylon absorbs moisture and bubbles during ironing — must be thoroughly dried. |
| PC (Polycarbonate) | 5-8% | 15 | 0.15 | Normal temp | PC has high melt temp — slow ironing prevents surface degradation. |
Slicer-Specific Setup
Cura
Search “ironing” in settings. Enable “Enable Ironing.” Four sub-settings appear:
– Ironing Pattern: Zig Zag (fastest, slight directional lines visible) or Concentric (smoother on round parts).
– Ironing Line Spacing: 0.1mm.
– Ironing Flow: 10% (adjust per material table above).
– Ironing Inset: 0.38mm — prevents ironing right to the edge, which can create a lip.
Cura also has “Iron Only Highest Layer” — enable this. Without it, Cura irons every top surface layer, including internal top surfaces like mounting bosses and recesses. These are invisible in the finished part and ironing them adds print time with zero benefit.
PrusaSlicer / OrcaSlicer
Under “Ironing” in the print settings:
– Ironing Type: “Topmost surface only” (equivalent to Cura’s “Iron Only Highest Layer”).
– Ironing flow: 10%.
– Ironing speed: 20 mm/s.
– Spacing between ironing passes: 0.1mm.
– Ironing angle: Leave at default (-1 for automatic per-layer rotation) or set to 0° for aligned finish.
OrcaSlicer adds “Ironing direction” — set to “All solid fill” direction to match the underlying layer orientation. Mismatched angles create a slight crosshatch pattern that’s visible in certain lighting.
When Ironing Makes Things Worse
Ironing is not universally beneficial. Skip it in these situations:
Curved top surfaces: Ironing only works on flat horizontal surfaces. On a domed or curved top, the nozzle either gouges the surface or floats above it. The slicer won’t warn you — it’ll try to iron anyway and you’ll get nozzle drag marks across the dome.
Text/logos on the top surface: Ironing smears small raised details. Embossed text thinner than 1mm line width gets partially melted into the surrounding surface and becomes illegible. Debossed text (cut into the surface) handles ironing better but the edges soften slightly.
Less than 3 top layers: Ironing adds heat to the top surface. With only 1-2 top layers, that heat penetrates to the infill and creates a visible pattern — the infill grid shows through the ironed surface. Always use 3+ top layers with ironing.
Small parts under 20×20mm: The nozzle spends proportionally more time on the perimeter vs. the center, creating uneven heat distribution. The edges overheat while the center is barely touched. Ironing small parts often creates a visible border effect.
What Most Makers Get Wrong
Mistake 1: Ironing every print without calibration. Default ironing settings in Cura (10% flow, 0.1mm spacing, 20mm/s) work for approximately half of PLA brands and fail for the other half. Silk PLA, matte PLA, and PLA+ all behave differently under ironing heat.
Consequence: You enable ironing, the surface looks worse than un-ironed, and you conclude “ironing doesn’t work.” The feature works — the defaults don’t work for your filament.
Fix: Run the 4-square calibration test (8%, 10%, 12%, 14% flow) for each new filament brand. Takes 15 minutes and gives you the correct ironing flow for that specific spool. Write the value on the spool label.
Mistake 2: Ironing walls and internal surfaces. Leaving “Iron Only Highest Layer” disabled causes the slicer to iron every horizontal surface inside the part — mounting bosses, internal shelves, support interfaces. None of these are visible in the final part, and ironing them adds 20-40% to total print time on complex parts.
Consequence: An 8-hour print becomes 11 hours with no visible improvement. The extra heat cycling on internal layers can actually cause slight warping on tall thin-walled parts.
Fix: Always enable “Iron Only Highest Layer” (Cura) or “Topmost surface only” (PrusaSlicer/OrcaSlicer). This ironing only applies to surfaces visible from the top.
Mistake 3: Ironing at the wrong temperature. Ironing uses the same nozzle temperature as the rest of the print. If you’re printing PLA at 215°C (hot to improve layer adhesion), ironing at 215°C can over-melt the surface and create a glossy, wavy finish instead of a smooth matte one.
Consequence: The ironed surface looks like melted plastic rather than smooth plastic. It’s shiny in patches and matte in others — the “zebra stripe” effect.
Fix: For PLA, run a separate ironing temperature test. Print at 200°C with ironing at 200°C, 195°C, 190°C, and 185°C. The correct ironing temperature produces a uniform satin finish. For most PLA, ironing at 5-10°C below print temperature looks best.
⚠️ Safety Notice: The printing recommendations in this article are for standard consumer 3D printers operating within their rated temperature ranges. Always ensure adequate ventilation when printing materials that emit fumes (ABS, ASA, nylon, PC). Verify your printer’s thermal runaway protection is enabled and functioning — ironing extends print time and increases total thermal load on the printer. Check that your printer meets 2026 electrical safety certification requirements for your region.
Related Guides
Ironing is the final surface pass, but layer quality starts with first-layer adhesion — see our First Layer Calibration guide if your bottom surface is the problem. Over-extrusion on normal layers creates ridges that ironing can’t fix — see our Over-Extrusion Diagnosis. And for comparing slicer ironing implementations across Cura, PrusaSlicer, and OrcaSlicer: OrcaSlicer vs PrusaSlicer vs Cura comparison.
Recommended Product
Ironing exposes every inconsistency in your nozzle and hotend. A quality nozzle with a polished internal bore produces cleaner ironing results than a rough factory brass nozzle. The uavmodel hardened steel nozzle kit (0.4mm, 0.6mm, 0.8mm) maintains consistent internal geometry through hundreds of print hours, and the polished interior produces noticeably smoother ironed surfaces than unpolished brass. Stock up on your next filament order at uavmodel.com.