A 1 mm shell can be enough for an aesthetic cover and fail immediately on a bracket subject to vibration. Understanding how to calculate wall thickness therefore means translating the function of the part into a producible geometry, not choosing a standard value to apply to every CAD file.
In professional 3D printing, the minimum thickness depends on the technology, the material, the production orientation and the local geometry. But nominal thickness is not enough: ribs, fillets, internal voids, tolerances and concentrated loads can radically change the behaviour of the component. The right approach is to design the wall together with the required function, checking the file before production.
What wall thickness depends on
Wall thickness is the distance between two opposite surfaces of the model. In a hollow part, it is the material that remains between the inside and the outside; in a solid structure with lightweighting, it is the thickness of the webs that define the cavities. In CAD it can be controlled with thickness analysis tools, sections and local measurements.
The initial question is not only "how thin can I print?", but "what load does this wall have to carry and in which direction?". A thin wall may withstand distributed compression well, but deform under bending, impact or screw tightening. The intended use matters too: a form prototype, a component for functional tests and a small run for end use call for different design margins.
To choose the right value, assess these factors together:
- mechanical function of the component and type of stress;
- printing technology and selected material;
- height, unsupported span and curvature of the wall;
- presence of holes, screw seats, interlocks and changes of section;
- required finish and dimensional tolerance;
- operating conditions, including temperature, humidity, chemical agents and duty cycles.
A very tall, flat wall, for example, is more exposed to bending than a wall of the same size stiffened by curvature or ribs. Increasing thickness indiscriminately only partly solves the problem, while raising weight, production time and cost. In many cases it is more effective to add a fillet, a rib or a closed geometry.
How to calculate wall thickness in CAD
The calculation starts from the functional dimensions, not from the printer. If the part has to fit into a housing, the available external thickness is constrained. If it has to contain an internal volume, the basic relationship is simple:
`wall thickness = (external dimension - internal dimension) / 2`
The formula applies to symmetrical sections. If a box has an external width of 60 mm and an internal cavity of 56 mm, the two side walls measure 2 mm each. If the base has a different function from the side walls, it must be dimensioned and checked separately: it is not necessary for every side to have the same value.
When the model originates from a surface, the CAD Shell or Hollow command generates the wall from an offset. It is useful, but it does not replace the technical check. In tight radii, in areas with double curvature and in complex fillets, the offset can create areas thinner than the set value or self-intersections. Thickness analysis must therefore be carried out on the final solid, not only on the parameter entered in the command.
For components with variable sections, it is worth identifying the critical zones: the base of a shelf, the root of a tab, the edge of a hole, the transition between wall and rib. These areas, more than the central wall, determine the risk of breakage. A colour check in CAD quickly highlights local minima that are often not visible in the standard view.
Do not confuse wall, perimeters and infill
In FDM printing, wall thickness is also linked to the number of extruded perimeters and the line width. With a standard 0.4 mm nozzle, a wall designed at 0.8 mm can be made with two lines side by side. A 1.2 mm wall generally lends itself to three lines. The actual value, however, depends on the slicing profile, the extrusion width and the material.
Internal infill does not replace an adequate wall. High infill increases the support to the structure, but resistance to impact, threads and local bending depends mainly on perimeters, layer orientation and external geometry. For a functional shell, it is often preferable to increase the outer shells instead of taking the infill to 100%.
In SLS and MSLA the reasoning is not tied to slicer perimeters in the same way, but the stability of the wall and the ability of the geometry to hold up during production, cleaning and post-processing remain central. Very thin walls may be achievable, but are not always suitable for a part intended for handling or repeated use.
Indicative thicknesses for FDM, SLS and MSLA
There is no single minimum thickness valid for all technologies. The values below are a design starting point, to be checked against the specific geometry and material.
For FDM, a functional wall generally starts from 1.2–1.6 mm with a 0.4 mm nozzle, especially if it must be made of several full perimeters. For covers, form elements or unstressed details you can go lower, but sensitivity to deformation, impact and surface imperfections increases. If clips or snap-fits are present, the material and layer direction become decisive: TPU, PETG and PA behave differently from PLA or rigid resins.
For SLS in PA12, 1–1.5 mm can be a reference for non-structural walls that are well supported by the geometry. For functional parts, shells subject to bending or large surfaces, it is often more prudent to start from 2 mm and introduce stiffeners where necessary. The technology allows geometric freedom and internal cavities, but requires attention to the removal of unsintered powder: a closed volume with no evacuation holes is not a producible solution.
For MSLA, resins allow fine detail and accurate surfaces, but some formulations are stiffer and more brittle than thermoplastic polymers. Walls between 1 and 2 mm can work for many models, while for components subject to impact, screwing or continuous use it is advisable to increase the thickness and choose a suitable engineering resin. A thin wall in a standard resin can look perfect straight off the printer, but break during assembly.
If the CAD file is set up in inches, it is worth converting and checking the values before export: 1/16 in corresponds to about 1.59 mm. In additive production, working with explicit metric dimensions reduces ambiguity during checking, slicing and dimensional inspection.
Reinforcing without making the part heavier
When a wall has to carry loads, increasing the thickness is not the only option. Ribs are often the most efficient solution because they increase the second moment of area of the section with limited material use. A rib should blend into the wall with adequate radii and avoid abrupt terminations, which concentrate stresses.
Fillets are part of the calculation too. A sharp internal corner at the base of a wall creates a critical zone, especially in the presence of vibration or alternating loads. A consistent radius distributes stresses better and improves manufacturability. For cantilevered elements, it can be useful to close the geometry with a folded edge or turn a flat wall into a U-shaped section.
Pay attention to screw seats. If a self-tapping screw enters a wall that is too thin, failure can occur along the line of the hole. In these cases it is preferable to design a dedicated boss, a threaded insert, a bush or a local reinforcement. Sizing must consider screw diameter, tightening torque, number of cycles and distance from the edges.
Technical check before sending the file
An effective check combines automatic analysis with a functional reading of the component. Before export, check that the model is closed, with no inverted surfaces, intersections or walls below threshold. The STEP format retains the native geometry and is preferable for a full technical check; STL can be sufficient for production, provided it has a consistent resolution and is free of mesh errors.
The final choice must be validated on the real case. A 1.5 mm wall can be ideal for a PA12 housing and insufficient for a long lever under repeated load. Likewise, a 3 mm wall can be oversized if a targeted rib achieves the same stiffness with less mass.
When the part has a critical function, sharing loads, operating environment, assembly and finish from the outset avoids late corrections. Doppialinea can check the manufacturability of the file and indicate the most suitable compromise between thickness, material, technology and delivery times. The right wall is not the thickest one: it is the one that takes the component from CAD to its intended use with repeatable quality.
