Seam Position Explained: Hide or Align Your Layer Seam

Seam position in 3D printing is the setting that decides where each layer's outer loop starts and ends, which is where the visible vertical seam forms. Slicers offer nearest, aligned, rear and random placement. Aligned or rear stack the seam into one tidy line, while random scatters it.

This guide explains what each option does in OrcaSlicer, PrusaSlicer and Cura, and how to hide the seam or put it where you want it. It is based on the slicer makers' own documentation, not on our own test prints.

What is a seam in 3D printing?

A seam is the small blemish where the nozzle begins and finishes each closed outer loop of a layer. A printer cannot start and end a loop without a join, so every layer has one. Prusa's help article states it plainly: "With the FFF/FDM technology, it is not possible to eliminate the seam." The goal is to control where it lands and how visible it is.

Cura's setting description explains the cause: when paths in consecutive layers start at the same point, a vertical seam may show on the print. Stack the starts and you get a line. Scatter them and you get scattered blemishes instead.

What are the seam position options?

The names differ slightly by slicer, but the ideas are the same. This table summarizes the maker documentation.

In Cura the first option in the file is internally called back but labeled "User Specified", and the default in the definitions is Sharpest Corner. Cura also has a separate Seam Corner Preference with Hide Seam, Expose Seam, Hide or Expose Seam and Smart Hiding choices.

Which seam position hides the seam best?

For most parts, aligned or rear hides the seam best, because a single straight line along a corner or the back face is easy to ignore. Nearest also hides well on models with sharp corners. Prusa says that on a model with sharp corners, Nearest "will make the seam effectively invisible." The OrcaSlicer wiki says Aligned Back, Aligned or Back typically work best, especially with seam painting.

Random is the odd one out. Prusa says it makes the seam less noticeable but the surface less smooth, and that it "makes little sense" on models with sharp edges, although it is viable for cylindrical shapes without sharp edges.

How do you choose a seam position?

• Display piece with a front: use Aligned Back (OrcaSlicer) or Rear (PrusaSlicer) and rotate the model so its least important face points to the back.
• Box or bracket with sharp corners: use Aligned or Nearest so the seam sits inside a vertical corner.
• Smooth round object: there is no corner to hide in, so paint the seam to one spot or accept Random.
• Part that carries load: OrcaSlicer's wiki says Random may suit parts needing higher strength, such as a pin for a hole, because it spreads the weak points.

Layer thickness changes how much any of this matters. Taller layers make a more obvious seam line, so see layer height explained.

Can you paint the seam by hand?

Yes. Prusa says that from PrusaSlicer 2.3 the seam painting tool gives detailed control over seam placement, and OrcaSlicer supports seam painting too. You brush on enforced or blocked areas of the model, so the slicer puts the seam inside a groove, behind a feature or along a hidden edge. It is the most reliable fix for round parts. If you are new to these tools, read our guides to OrcaSlicer and PrusaSlicer.

What are scarf seams and seam gap?

A scarf seam is a way to make the join nearly disappear instead of just moving it. OrcaSlicer's wiki says scarf joints adjust extrusion flow at seam points to create a smooth overlap between the start and end of each loop. Its settings include a type of None (default), Contour or Contour and hole, a scarf length that defaults to 20 mm, and a slow joint speed, recommended under 100 mm/s.

The same wiki says scarf joints are never applied on the first layer, in spiral vase mode or on belt printers, and that they may slightly increase print time and work less well on sharp corners and overhangs. Prusa gives the same caveats.

Seam gap sets the space between the two ends of the loop. A larger gap reduces seam bulging and a smaller gap makes the seam less visible. OrcaSlicer's wiki says that for a well-tuned printer with pressure advance and retraction, 0 to 15 percent is typically optimal. Staggered inner seams, an advanced option there, offset each inner wall's seam so weak points do not line up.

Why is my seam still ugly?

If the seam is a bulge or a blob rather than a thin line, placement is not the main problem. OrcaSlicer's wiki says to calibrate pressure advance first because it strongly affects seam start and end quality, and Prusa notes that Linear Advance and extrusion multiplier calibration affect how visible the seam is. Read what pressure advance is, how to fix blobs and zits and retraction settings explained.

Wall order matters too. The OrcaSlicer wiki says inner-outer-inner order is generally best for seams, followed by inner-outer. For a printer-wide checklist, see the calibration guide. If you want to avoid the seam entirely, Prusa says vase mode does, but you are limited to one perimeter and no infill. For a choice of slicer, see our comparison pages.