Z seam: the visible line on an FDM print
On normal FDM perimeter loops, every closed path needs a start and end point. That transition can create a visible vertical mark commonly called the Z seam. It can be reduced or deliberately positioned, but normal closed perimeters cannot eliminate it completely.
Why does the seam exist?
At every layer: perimeter starts → travels around the model → ends. Small material differences can become visible at that transition.
Round models show it more clearly
A rectangular box offers corners where the seam can be hidden. A smooth cylinder has no natural corner, so the seam is easier to see.
Seam placement
Depending on the slicer, options may include:
- nearest edge
- aligned
- rear
- random
- seam painting
Random is not automatically invisible
Random placement removes the single vertical line but spreads small marks across the surface. For functional visible surfaces, a deliberately placed seam can look better.
Flow and pressure control
Poor extrusion tuning can make the seam more visible. Do not use seam placement to hide a broader extrusion problem.
Spiral vase mode
Vase mode can avoid the traditional seam, but only for suitable continuous single-wall geometry.