Wall Thickness

What is wall thickness, and why does it have a minimum?

Wall thickness is the thickness of the solid shell that forms the outside of your part — and the internal dividers, if it has any. Most prints are not solid blocks: they are a shell of walls around a lighter infill. The walls do most of the work of holding shape and bearing load.

Every printing process has a minimum wall thickness below which a wall cannot be made reliably. Go under it and the result is not 'a thinner wall' — it is gaps, missing material, or a wall too fragile to survive handling. Understanding this floor is the difference between a model that looks fine on screen and one that actually prints.

How does nozzle size set the minimum wall in FDM?

In FDM (the Bambu Lab process), plastic is laid down in lines of a fixed width, set by the nozzle. A standard nozzle is 0.4 mm, which produces an extruded line roughly 0.4–0.45 mm wide. A wall has to be at least one line wide to exist at all.

But one line is fragile. A reliable structural wall is usually two or more lines side by side. This leads to the single most useful design rule on this page: make walls a multiple of your line width. With a 0.4 mm nozzle that means walls around 0.8 mm, 1.2 mm, 1.6 mm, and so on. When a wall is a clean multiple of the line width, the slicer fills it perfectly with whole lines; when it is an awkward in-between value, the slicer is left with a thin gap it fills poorly or skips.

[VAHVISTETTAVA: tarkat luvut Bambu Lab X1:n oletusasetuksilla — viivanleveys ja suositeltu minimi. Korvataan Miklaksen testillä.]

How thick should a wall be — for strength, or just for looks?

The right thickness depends on the wall's job. A decorative surface that bears no load can be near the minimum — just enough to print cleanly. A functional wall that holds weight, takes stress, or gets handled needs more material: extra perimeters, or a deliberately thicker shell along the load path.

Think about how force travels through the part. A box carrying weight needs stronger walls and floor than a box that only holds a light necklace. The same shape can be 'over-built' or 'just enough' depending on what it must survive — and choosing deliberately is what separates designing from guessing.

Thicker is not automatically better: every extra millimetre of wall costs print time and material, and very thick solid walls can even introduce their own problems. The goal is enough, matched to purpose.

What actually happens if a wall is too thin?

The slicer tries to fit lines of material into the wall you drew. If the wall is thinner than a line, there is nowhere to put material — the slicer leaves it empty, and your wall simply is not printed.

If the wall is between one and two line widths, the slicer often cannot fit a clean second line, leaving a gap between the outer perimeters — a weak, sometimes visibly hollow seam.

And even when a too-thin wall does print, it may be so fragile that it cracks during removal from the plate, handling, or normal use. The failure often shows up after printing, not during it.

Does the rule change for resin, metal, and other processes?

Yes — the concept is universal but the numbers are not. Resin (SLA) printers resolve much finer detail, so their minimum walls can be considerably thinner than FDM. Metal powder processes have their own constraints driven by the powder, the laser, and thermal stress.

So treat any specific millimetre value as belonging to a specific process. The transferable skill is the habit: find the minimum for the process you are using, and design walls deliberately above it. The per-process numbers live in the process guides.

[VAHVISTETTAVA: resiinin ja metallin tyypilliset minimit — täytetään prosessisivuja tehtäessä, lähteestä + 3D Formtechilta.]

How do you find the real minimum for your own printer?

Do not trust a number from the internet — including this page. Every printer, nozzle, material, and speed combination behaves a little differently. The reliable way is a wall thickness test print: a row of walls at increasing thickness, printed once, then inspected to see which ones came out clean and strong.

Because you can now model parametrically, you can generate this test yourself in OpenSCAD — a `for` loop of thin walls at 0.4, 0.8, 1.2, 1.6, 2.0 mm. Print it, look at which walls printed solid versus gappy or fragile, and you have your real minimum — measured, not guessed.

Once you know that number, write it down and design to it. This single test answers a question that a hundred tutorials only approximate.