How thin can a 3D printed wall be?
Why hollow models need a minimum wall thickness, how to choose one, and what happens when a wall is thinner than the printer's nozzle.
Hollowing a model is the single biggest saving available to a young designer. A solid 40 mm cube uses a lot of plastic and takes hours; the same cube with a 2 mm wall looks identical from outside and prints in a fraction of the time. The question is how thin that wall can go.
The nozzle sets the floor
A printer lays plastic in lines about as wide as its nozzle — most commonly 0.4 mm. A wall has to be at least one line thick, and a wall exactly one line thick is fragile and often patchy. Two lines, so around 0.8 mm, is the realistic minimum for something that must survive being handled. Three lines, around 1.2 mm, is a sensible default for anything a child will carry in a bag.
- Under 0.8 mm: the slicer may quietly skip it, leaving a gap where you drew a wall.
- 0.8–1.2 mm: prints, but flexes and can crack.
- 1.2–2 mm: strong enough for most classroom objects.
- Over 3 mm: rarely needed, and starts costing real time and plastic.
These figures assume a common 0.4 mm nozzle. Yours may differ, and no design tool that has not met your printer can tell you the right number. The habit worth teaching is checking the nozzle size rather than trusting a default.
Why the tool cannot check this for you
Measuring the thinnest part of an arbitrary solid is a genuinely hard geometry problem, and most design tools — including this one — do not attempt it. What a tool can honestly do is let you state the wall you want when you hollow something, and then say plainly that the figure is nominal. Treat a wall thickness as a decision you made, not a guarantee you were given.
The trap: a sealed hollow
If you hollow a shape completely and leave no opening, the space inside is sealed. Some slicers handle this fine; others fill it, or trap uncured material in resin printing. If the inside does not need to be sealed, leave a hole. It also lets you see your own wall, which is worth something.
Do it, don't just read it
This pairs with lessons inside the Studio, where the checkpoints tick because the design really has that property, and un-tick if you undo the work:
- Lesson 3 — Hollow It Out
- Lesson 10 — The Brief
Read next
Starting out
What is 3D printing?
How a 3D printer turns a design on a screen into an object you can hold — explained for children, parents and teachers, with no jargon.
Starting out
How to design your first 3D model
A first design from nothing to a saved file: choose a shape, give it real sizes, check it, and export it. About twenty minutes.
Designing well
Clearance and tolerance: making parts that actually fit
Why a 10 mm peg will not go into a 10 mm hole, how much gap to leave, and how to work out the right number for your own printer.