The Complete Guide to 3D Print Ironing for Perfect Results (2025)

Introduction

Almost every 3D printing fan has felt this disappointment: you pull a perfectly sized print off the bed, only to see ugly ridged lines covering the top surface. These lines are a normal part of how FDM (Fused Deposition Modeling) printers work, but they can make an otherwise great print look unfinished. The answer is a useful but often confusing slicer feature called "Ironing." This feature is made to get rid of these ridges, creating a smooth, almost factory-made finish right on your printer. This complete guide for 2025 explains exactly what is ironing in 3d printing, how it works, and how to set it up in any modern slicer program. We will look at its good and bad points, how it works with different materials, and how to fix the most common problems to get a perfect top surface.

1. What is Ironing?

A Simple Comparison

To understand what is ironing in 3d printing, think of a regular household iron smoothing wrinkles on clothes. The heat and pressure of the iron flatten the fabric fibers into a smooth surface. In 3D printing, the hot nozzle of the print head acts as the "iron" for the final plastic layer. It uses heat and careful movement to change a bumpy, lined texture into one smooth, flat surface. This happens automatically at the end of the print, so you don't need to do anything. It's a finishing step built right into the printing process.

How It Works

The way ironing works combines heat and a tiny amount of new material. Here's what happens step by step:

1. The printer finishes the final top layer of your model normally, laying down parallel lines of plastic.
2. Instead of moving away to end the print, the print head keeps the nozzle at exactly the same height as that final layer.
3. The nozzle then starts a second, careful pass over the entire top surface.
4. During this pass, the heat from the bottom of the nozzle remelts the tiny peaks of the just-printed lines.
5. At the same time, the extruder pushes out a very small, controlled amount of new plastic, called "ironing flow."
6. This newly melted plastic fills the valleys between the original lines. The movement of the hot nozzle smooths this melted material across the surface, joining the peaks and filled valleys into one smooth, uniform layer.

(Visual Cue: A diagram showing a cross-section of a top layer. "Before Ironing" shows separate lines with peaks and valleys. "After Ironing" shows a flat, filled-in surface.)

2. Should You Use Ironing?

The Good Things About Ironing

The main reason to use ironing is the huge improvement in surface quality. It offers several important benefits:

• Perfect Appearance: This is the main benefit. Ironing changes rough, lined top layers into glass-smooth surfaces. This greatly improves how display models, product cases, custom enclosures, and decorative items look, giving them a more professional, finished appearance.
• Gets Rid of Top-Layer Lines: It directly fixes one of the most obvious problems with FDM printing. For parts where a smooth top is important, ironing is the best solution.
• Better Feel and Function: An ironed surface doesn't just look good; it also feels nice to touch. This can be helpful for parts that need to make smooth contact with other parts or that people will handle often.
• No Manual Work After Printing: Getting a smooth finish without ironing often requires hours of sanding, filling, and painting. Ironing does this automatically, saving a lot of time and work. The part comes off the print bed already finished.

(Visual Cue: A high-quality, side-by-side comparison photo of two identical prints: one "Without Ironing" and one "With Ironing," showing the big difference.)

The Problems with Ironing

Despite its benefits, ironing shouldn't be used on every print. It has downsides that you need to think about:

• Much Longer Print Time: The ironing pass is done slowly and carefully to allow for proper heat transfer. For prints with large, flat top surfaces, this can add a lot of time to the total print, sometimes hours.
• Risk of Surface Problems: If the settings aren't set up correctly for your specific plastic and printer, ironing can make the surface look worse. It can cause scratches, blobs, too much material at edges, or a rough, melted texture.
• Possible Nozzle Problems: The combination of very slow movement and extremely low material flow can increase the chance of heat creep. Heat can travel up the plastic path, causing it to soften too early and block the nozzle, especially with temperature-sensitive plastics.
• Different Results with Different Materials: How well ironing works varies a lot between plastic types. What works perfectly for PLA might create a stringy mess with PETG. Each material needs its own tuned settings.

3. How to Set Up Ironing

Finding Ironing Settings

As of 2025, the ironing feature is standard in all major slicers, including Cura, PrusaSlicer, OrcaSlicer, and Bambu Studio. It's usually found in the settings panel under sections like "Quality," "Top/Bottom Layers," or "Finishing." If you can't find it, the easiest way is to use the slicer's settings search bar and type "ironing." This will immediately show all related options.

Understanding Key Settings

Setting up ironing properly requires balance. Understanding what each setting does is important to get a perfect finish instead of a melted mess.

• Enable Ironing
  This is the main switch to turn the feature on or off. Many slicers let you choose between "All top surfaces" and "Topmost surface only." The "Topmost" option is usually better, as it only smooths the final visible surface of the model, saving time by not ironing internal top surfaces that will be covered by more layers.

• Ironing Flow (or Ironing Flow Rate)
  This is probably the most important setting. It controls the percentage of plastic extruded during the ironing pass compared to normal printing. The goal is not to print a new layer, but to push out just enough material to fill the gaps between the lines of the last layer. A good starting point is 10-15%.

• Too High: Causes extra material to build up, creating a bumpy, rough surface, blobs, and scratches as the nozzle drags through the excess plastic.

• Too Low: Not enough material comes out to fill the valleys. The surface may look starved, patchy, or unchanged from a non-ironed print.

• Ironing Speed
  This setting controls how fast the nozzle moves during the ironing pass. It needs to be slow enough for heat to transfer but fast enough to be efficient and prevent heat-related problems. Common values range from 100 to 200 mm/s.

• Too Fast: The nozzle moves too quickly for the heat to effectively remelt and smooth the surface. The ironing effect will be minimal.

• Too Slow: Greatly increases print time and raises the risk of melting the surface too much, causing problems. It also increases the chance of heat creep and nozzle clogs.

• Ironing Line Spacing
  This controls the distance between each parallel line of the ironing pass. It should be smaller than your nozzle width to ensure complete coverage. A good starting value is often around 0.1mm to 0.2mm.

• Too Wide: The ironing pass itself will leave visible lines on the surface, defeating the purpose.

• Too Narrow: The nozzle repeatedly goes over the same area, which overworks the plastic and can lead to material buildup and a rough finish. It also adds unnecessary time to the print.

• Ironing Pattern
  This controls the direction of the ironing paths. The two most common options are Zig-zag and Concentric.

• Zig-zag: The nozzle moves back and forth in straight, parallel lines. This is the standard pattern and works well for most shapes.
• Concentric: The nozzle moves in concentric circles, spiraling outward or inward. This is ideal for models with circular top surfaces, as it avoids the sharp direction changes of a zig-zag pattern that can leave marks.

Recommended Starting Points

These settings are a safe, reliable starting point for standard material like PLA. Use them as a beginning and adjust for your specific printer and plastic.

4. How Different Materials Work

Material Guide

How well ironing works depends heavily on the type of plastic you're using.

• PLA (Polylactic Acid)
  PLA is perfect for ironing. Its relatively low melting point and excellent heat stability allow it to remelt and smooth out beautifully with little trouble. It's the most forgiving material and the best one to use when first learning to adjust your ironing settings. It creates a shiny, smooth finish.

• PETG (Polyethylene Terephthalate Glycol)
  Ironing PETG can work but is much more challenging. PETG is very sticky when melted and tends to pick up and drag material across the surface, causing scratches and blobs. Success requires careful tuning, often with slightly lower flow and faster speed than PLA. A very clean nozzle is essential to prevent material from sticking to it.

• ABS/ASA (Acrylonitrile Butadiene Styrene / Acrylonitrile Styrene Acrylate)
  Both ABS and ASA work very well with ironing, often creating a superior matte, smooth finish that looks very professional. However, these materials need a well-tuned printer with a heated bed and a full enclosure. The longer print time caused by ironing increases the risk of warping and layer splitting if the temperature around the printer isn't properly controlled.

• TPU & Other Flexible Materials
  Ironing is generally not recommended for flexible plastics like TPU. The pressure and friction from the nozzle passing over the surface can easily deform the soft material. Instead of smoothing it, the nozzle tends to drag, stretch, and tear the top layer, creating a very poor finish.

• Special Materials (Silk, Wood, Carbon Fiber)
  Use extreme caution. Silk plastics, which are valued for their unique shine, can lose that characteristic sheen and become dull when ironed. Abrasive materials like wood-fill, carbon fiber-fill, or glow-in-the-dark increase the risk of nozzle clogs during the slow, low-flow ironing moves. They will also greatly speed up the wear on a standard brass nozzle.

5. Fixing Common Problems

Your Ironing Problem-Solving Guide

When ironing goes wrong, the results can be frustrating. Here's how to identify and fix the most common problems.

• Problem 1: Scratches or Gouges on the Surface
• Common Causes: The Ironing Flow is too high, creating excess material that the nozzle then drags through. Your Z-offset may also be too low, causing the nozzle to physically plow through the top layer.

• Solutions: Decrease the Ironing Flow setting in small steps (like 2%). Check your printer's first layer setup and Z-offset to make sure the nozzle isn't too close to the bed, which can affect the top layer too.

• Problem 2: Bumpy Edges or Blobs at Corners

• Common Causes: This is often a sign of too much material that happens when the nozzle slows down to make a sharp change in direction. The plastic pressure in the hotend isn't being properly managed.

• Solutions: The best solution is to set up your printer's Pressure Advance (for Klipper firmware) or Linear Advance (for Marlin firmware). These features manage extruder pressure ahead of time. Some slicers also offer an "Ironing Inset" setting, which pulls the ironing path slightly away from the outermost edge to prevent material from spilling over.

• Problem 3: The Surface Looks Starved or Unchanged

• Common Causes: The Ironing Flow is set too low to fill the gaps. Another major problem is wet plastic. Moisture in the plastic turns to steam in the hotend, creating bubbles and preventing smooth plastic flow.
• Solutions: Increase the Ironing Flow in 2% steps until the surface looks uniform. Most importantly, dry your plastic. Even brand-new plastic can contain moisture. Using a dedicated plastic dryer is one of the best steps you can take to improve all aspects of print quality, especially for surface finishes.

Pro Tip for Testing

To avoid wasting time and plastic, don't test your ironing settings on a large, multi-hour print. Download or create a small, flat "test coin" model—a simple disc about 20-30mm across and a few millimeters high. Printing just the top layer of this model with different ironing settings lets you quickly test and adjust. You can test a dozen setups in the time it takes to print one large part, quickly finding the perfect settings for your material.

6. Comparing to Other Methods

Is Ironing Always Best?

Ironing is a powerful tool, but it's important to know where it fits among other surface smoothing techniques.

• vs. Sanding
  Ironing is an automatic process that only affects top-facing horizontal surfaces. Sanding is a manual process that removes material and can be used on any surface of the print. Ironing keeps the part's original size, while sanding physically changes it.

• vs. Vapor Smoothing (for ABS/ASA)
  Ironing is a safe, in-slicer process that uses heat to smooth only the top layer. Vapor smoothing is a dangerous post-processing step that uses chemical solvents (like acetone for ABS) to melt the entire outer shell of a model. While vapor smoothing affects all surfaces, it can also soften or remove fine details, which ironing doesn't do.

• vs. Epoxy/Resin Coating
  Ironing improves the existing surface of the print while keeping its size. Applying a coating like epoxy or UV resin adds a thick, durable new layer to the part. This completely changes the surface properties, size, and weight of the model. Coatings are excellent for strength and a shiny finish but are a separate, messy, and manual step.

In summary, ironing is the most integrated, accessible, and precise method for getting a smooth top surface directly from the 3D printer, without manual work or external processes.

Conclusion

Ironing is a game-changing slicer feature that offers a direct path to professional-quality top surfaces on FDM 3D prints. It represents a trade-off, balancing the promise of an incredible, factory-like finish against the costs of increased print time and the need for careful setup. It's not a magic solution that works perfectly right away, but rather a powerful tool that rewards a small investment in tuning. Once you master it, it raises the quality of your prints to a new level, eliminating one of the most persistent problems of the technology. We encourage you to start with the recommended settings, use a test model to experiment, and unlock the potential for truly perfect finishes on your 2025 projects.

Have you mastered ironing on a tricky material? Share your go-to settings and experiences in the comments below to help the community