3D Printing Ironing: How to Get Glass-Smooth Top Surfaces
If you've ever looked at a finished print and thought the top surface looks rough and lined compared to the sides - ironing fixes that. It's a post-processing pass the slicer adds after the final top layer, and when it's set up correctly, it turns a textured surface into something that looks almost injection-moulded.
It's one of those features that sounds fiddly but takes about two minutes to set up, and the results speak for themselves.
What Is Ironing?
Ironing is an extra pass the printhead makes over the top surface after it finishes the final layer. The nozzle moves slowly back and forth across the surface, either extruding a very small amount of filament or nothing at all, remelting and smoothing the top layer as it goes.
The effect: instead of parallel ridged lines from the last top layer, you get a flat, smooth, slightly glossy surface.
When Ironing Is Worth Using
Ironing works best on:
- Flat horizontal top surfaces
- Decorative prints where appearance matters
- Prints with large exposed top areas (coasters, plaques, cases, tiles)
- Models where a clean surface finish is part of the design
It's less useful on:
- Curved top surfaces (the nozzle can't follow complex curves cleanly)
- Functional prints where you don't care about aesthetics
- Very small flat areas (the ironing pass is short and makes little difference)
How to Enable Ironing in Your Slicer
OrcaSlicer / BambuStudio
Quality settings > Ironing > Enable ironing. Set to "Top surfaces only" to start.
PrusaSlicer
Print settings > Infill > Ironing > Enable ironing.
Cura
Search "ironing" in settings (make sure All settings are shown). Enable "Iron top surface".
Ironing Settings Explained
Ironing Flow Rate
The percentage of normal extrusion used during the ironing pass. Lower flow means the nozzle is mostly just remelting existing plastic rather than adding new material.
- Too low: the surface still looks textured, not enough heat transfer
- Too high: you're depositing extra plastic, causing raised lines or blobbing
- Typical starting point: 10-15% for PLA, 15-20% for PETG
Ironing Speed
How fast the nozzle moves during the ironing pass. Slower means more time for heat to transfer and flatten the surface.
- Typical starting point: 50% of your normal print speed
- If results are inconsistent, slow it down further
Ironing Line Spacing
How far apart the ironing passes are. Wider spacing is faster but leaves more texture. Tighter spacing is slower but smoother.
- Typical starting point: 0.1-0.15mm (most slicers default to around 0.1mm)
Ironing Pattern
Most slicers offer concentric or linear options. Linear (back and forth) is the most common and works well for most shapes. Concentric follows the outer edge of the surface inward, which can look good on circular parts.
Finding Your Ideal Settings
The best way is to print all four settings side by side using the Ironing Test at tools.print3dbuddy.com. It prints four flat tiles - one with no ironing as a baseline, then 10%, 15%, and 20% flow - so you can see the difference directly.
Otherwise, start at 15% flow and 50% speed, run a quick test tile, and adjust from there.
Common Ironing Problems and Fixes
Still looks rough after ironing
- Flow too low - increase by 5%
- Speed too fast - reduce to 40% of print speed
- Nozzle temp too low - try adding 5-10°C for the ironing layer
Visible ridges or raised lines on the surface
- Flow too high - reduce by 5%
- Line spacing too wide - tighten to 0.08-0.10mm
Blobs or zits on the ironed surface
- Retraction not triggering during ironing passes - check slicer settings
- Filament moisture - dry your filament before printing
Ironing takes forever
- Normal - ironing adds 20-40% to print time on large flat surfaces
- Reduce to "top surfaces only" if you have it set to all layers
- Increase line spacing slightly (0.15mm instead of 0.10mm)
Does Ironing Work With All Filaments?
- PLA: Works extremely well. Most consistent results.
- PETG: Works well but needs slightly higher flow and is more prone to stringing during the pass. Make sure your retraction is dialled in.
- ABS/ASA: Works, but the surface tends to have more variation. Enclosure helps.
- TPU: Not useful - soft surfaces don't respond to ironing in a meaningful way.
Getting Ironing Right by Material
Each filament behaves a bit differently during the ironing pass.
PLA gives the most consistent results. The temperature window is narrow enough that the nozzle remelts the surface without over-depositing. Start at 15% flow and 50% speed.
Silk PLA tends to blob slightly during ironing because the additives lower viscosity. Try reducing flow to 10% first. If the surface still looks rough, slow the ironing speed down further before increasing flow.
PETG works but stringing during the ironing pass is common. Make sure retraction is correctly set and run the ironing at the lower end of your PETG temperature range. Some people drop temperature by 5-10°C specifically for the ironing layer using custom G-code in their slicer, though this complicates the setup.
ABS and ASA can iron reasonably well, but warping around the base of the model during a long print can disrupt the ironing pass if the model is partially lifting. An enclosure keeps things stable enough for it to work.
TPU doesn't benefit from ironing. The soft surface just deforms under the nozzle rather than smoothing.
Ironing and Print Orientation
Ironing only smooths flat horizontal top surfaces. It can't do anything useful for angled or curved surfaces because the nozzle moves in a flat plane and can't follow a slope.
If a model has an important angled surface that needs to look clean, the fix is print orientation rather than ironing. Rotate the model so that surface becomes a flat top, then print it that way, even if it means adding supports elsewhere. The ironing result on a properly oriented flat surface will look better than any other post-processing approach for most materials.
For models with multiple important faces at different angles, sanding or acetone smoothing (for ABS) may be more practical.
Multi-Colour Printing and Ironing
If you're printing multi-colour models using filament swaps or a multi-material system, ironing over colour-change layers can drag small amounts of the previous colour across the freshly deposited surface during the ironing pass.
The simplest solution is to disable ironing for the specific layers that sit directly above a colour change. Alternatively, make sure your colour-change purge is thorough enough that the nozzle is fully cleared before the ironing layer begins.
Is Ironing Worth It?
For decorative prints, yes. The difference between an ironed and unironed flat top is immediately visible and gives prints a much more finished look.
For functional prints, it's usually not worth the time. A bracket or a tool holder doesn't need a polished top face.
The one thing to be aware of: ironing adds print time, sometimes significantly on large flat areas. Run it on the prints where it counts.
Try It Yourself
The Ironing Test at tools.print3dbuddy.com gives you all 4 tiles in one STL - no ironing, 10%, 15%, and 20% flow. Print them all at once, compare the tops, and you'll have your ideal setting in under 30 minutes.
