How thick is thick enough — and when a rib beats a solid chunk. The numbers below are what our machines hold, not theory.
An FDM nozzle draws walls in 0.4 mm strokes. A 0.8 mm wall is two strokes back-to-back — the thinnest construction that's actually solid. Below that the slicer either drops to a single fragile pass or leaves a gap down the middle of the wall, and the part snaps along it like perforation.
That makes 0.8 mm the absolute minimum for anything — a label tab, a cosmetic shroud, a clip you'll bend once. The moment a wall does work, go thicker.
two perimeters — cosmetic features only
enclosures, covers, housings
brackets, mounts, anything bolted
tools, jigs, parts that get dropped
Strength in an FDM part lives mostly in the perimeters — the solid outline of each layer. Once a wall is thick enough for four to six perimeters (about 2.4 mm), making it thicker mostly adds infill, which adds grams, which adds dollars, while the stiffness gain flattens off.
If a 3 mm wall still flexes more than you want, the fix is geometry, not bulk: add a rib, a flange, or a corner gusset. You get far more stiffness per gram — and since we price by the gram, stiffness per gram is stiffness per dollar.
A flat plate that flexes wants a rib — a thin wall standing perpendicular to the surface, running along the direction of bending. One rib a few millimetres tall can out-stiffen a doubling of wall thickness at a fraction of the weight.
Make ribs 60–80% of the main wall's thickness, no taller than about four times their own thickness (taller ribs buckle), and land them with a small fillet where they meet the plate — sharp internal corners are where cracks start, in printed plastic the same as in moulded.
thinner than the wall it stiffens
taller ribs buckle instead of stiffening
kills the stress riser where rib meets plate
If you've come from resin printing or CNC, the instinct is to shell your part in CAD to save material. With FDM, don't. Send the part solid: the slicer automatically fills the interior with sparse infill, and the quote prices the grams the part actually needs — you're never paying for a solid block.
Hand-hollowed parts often print worse: internal shells create unsupported ceilings and trapped overhangs the slicer has to fight. Leave the inside to us; if a part genuinely needs full density (say, a fixture you'll tap threads into), mention it and we'll quote it that way.
Leave parts solid in CAD. Infill is automatic, and the price is computed from the grams your part needs — not bounding-box volume.
Tall, thin, free-standing walls wobble as the nozzle passes and print rippled — brace them to something or thicken the top. Wide thin fins and large flat floors want to warp as they cool, especially in ABS and ASA; ribs, rounded corners, and consistent thickness all help.
And keep wall thickness consistent where you can. A 1 mm wall meeting a 5 mm boss cools at different rates and pulls itself out of shape. Step thickness changes gradually, or break the part into consistent regions.
Drop an STL, STEP or 3MF and the quote applies every rule in this guide — mesh check included, GST included.