Short answer
Below 1.2 mm a wall is fragile and may not print reliably. Two millimetres is a sound general minimum, three to four for anything carrying load. Adding a rib is almost always better than making everything thicker.
The nozzle sets the floor
Our machines run a 0.4 mm nozzle, so every wall is built from lines roughly 0.4 mm wide. That gives you a practical grid: a 0.8 mm wall is two lines and has no interior at all, 1.2 mm is three, 1.6 mm is four. Ask for 0.9 mm and the slicer has to round to something it can actually produce, usually leaving a gap or an over-thin skin.
Designing walls in multiples of 0.4 mm is a free improvement. It costs nothing and removes a whole class of print artefacts.
Figures that work in practice
| 0.8–1.2 mm | Decorative shells, non-structural covers, parts nothing pushes against. Flexible and easy to crack. |
|---|---|
| 1.6–2.0 mm | General enclosures, trays, housings. A sound default when nothing is loading the part. |
| 2.4–3.2 mm | Brackets and mounts carrying light to moderate load. Where most functional parts should sit. |
| 4 mm and above | Heavier loads, or anywhere a screw threads directly into the plastic. |
Why ribs beat thickness
Doubling a wall from 2 mm to 4 mm roughly doubles the material in that wall. Adding a 2 mm rib across the same panel adds a fraction of that material and stiffens it far more, because stiffness rises with the cube of depth. A flat plate bends easily; the same plate with a spine down the middle barely moves.
This is why an injection-moulded part is full of thin ribs rather than thick slabs, and the same logic applies to printing — with the bonus that ribs cost you material and time you would otherwise spend on bulk.
Bosses, screws and inserts
Where a screw goes into plastic, the wall around it wants to be at least twice the screw diameter thick. An M4 screw wants roughly 4 mm of material around the hole. Less than that and the boss splits the first time someone over-tightens it.
For anything that will be undone and redone repeatedly, a threaded brass insert melted into the plastic is far more durable than a screw cutting its own thread. Design the hole to the insert manufacturer's dimensions and it will outlast the part.
Avoid sudden changes in thickness
A thin section meeting a thick one concentrates stress exactly at the join, and that is where the part will break. Blend between them with a chamfer or a fillet rather than a step. The same applies to sharp internal corners: a small radius costs nothing and removes the crack starter.
How to check your model quickly
Most CAD packages have a thickness analysis tool that will shade anything under a threshold. Set it to 1.2 mm and look for red. If you do not have that, slice the model in any free slicer and look at a layer preview through the thin areas — anywhere the slicer produces a dotted or broken line is somewhere the printer will struggle.
What this means when you order
If a wall in your model is too thin to print properly, we will tell you before we start rather than send you something that snaps in the post.
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