In 3D printing the WALL THICKNESS refers to the distance between one surface of your model and the surface perpendicularly opposite it.
This should not be confused with the MINIMUM DETAIL size which relates to non structural parts of your design. An example of this might be a surface texture or decorative buttons or text on your design.
However, creating a sturdy 3D printed design is more complex than meeting the minimum wall thickness requirements for any given material. These values are more aligned with the minimum resolution of the different printers than a value that is geared towards a structural recommendation. Producing a durable product has a lot to do with the design of the object, the surrounding material and whether your design is self supporting.
The minimum wall thickness values are as follows:
Durable Plastic - 1mm / 0.04"
Durable Gloss Plastic - 1.5mm / 0.06"
Stainless Steel and Gold Plate - 3mm / 0.12"
Take this small espresso cup with a wall thickness of 1mm as an example. In this instance 1mm is fine because the large surface area is self supporting. As the cup gets bigger though, the wall thickness will need to increase proportionately in order to remain self supporting.
Whereas a "wireframe" design like this tiny upside down table with unconnected legs or the cage below are risky. A wall thickness of 1mm is not enough because the surface area is low and the legs lack surrounding material that would otherwise help to support them. These are possible to print based on the printers resolution but will likely break in shipping, handling or during it's intended use.
Having all the ends are connected and supported in all directions like this example of the cage is a little better. In this case the ends of the wires self-support the overall design. However, the "wireframes" broke over time through general use/handling so 1mm would not be a durable long term
Generally the minimum wall thicknesses for unsupported wireframe structures (eg bits that stick out and have no end connection) should be 2 - 3 times the materials minimum wall thickness.
The minimum wall thicknesses for self-supporting wireframe structures (eg cage structure) should be 1.5 - 2 times the materials minimum wall thickness.
Tips for making wireframe structures stronger:
Avoid sharp corners. Think tree branches, transition one surface into the other smoothly.
Tapering your design so it is larger at the base where it connect to the other surface.
Keep within the suggested wall thickness to height ratios for prong designs discussed here
Design prongs as separate pieces that can be attached later.
It is best to err on the side of caution with the wall thicknesses you choose for a wireframe structural element. And as always prototyping and product testing is the best way to tell for sure if your design is up to scratch.
Want to push the limits? Find out how low you can push the minimum wall thickness values at your risk.