Design guide
Orientation & strength
FDM parts are anisotropic, they're stronger across the print plane than between layers. Orient the part so loads travel through layers, not across them.
Layers are a grain direction
Think of an FDM part like plywood: very strong in the plane of the layers, weaker across them. A bracket loaded across the layer lines (Z) can be 30-45% weaker than the same bracket loaded in plane (XY).
The fix is almost always orientation, not material. The same PLA part can be twice as strong simply by laying it down differently on the bed.
Layer adhesion per material
The lower the number, the more orientation matters. PETG is the most isotropic common material, its layers fuse very well, while carbon-fibre composites are the least, because the fibres only reinforce in-plane.
| Material | Z strength vs XY | Practical tip |
|---|---|---|
| PLA | 65% | Print load-bearing features in plane, not stacked across layers. |
| PETG | 75% | Best layer adhesion of the common materials, closer to isotropic. |
| ABS | 60% | Print in an enclosed chamber; cold drafts wreck layer bonding. |
| ASA | 60% | Same as ABS, enclosure matters. |
| PA-CF | 55% | Fibres only reinforce in-plane. Orient critical loads in XY. |
| TPU | 70% | Slow print speeds give the best layer fusion. |
Approximate tensile strength in Z as a percentage of the in-plane value, default print profiles.
Orientation rules of thumb
- Identify the primary load path in the part. Orient so the load runs along layers, not across them.
- Threaded inserts and screw bosses should pull along the layers, not across them. A boss printed standing up will shear off; lying down, it's several times stronger.
- Long, thin features (clips, snap-fits, levers) should lie flat on the bed. A clip printed upright snaps on the first flex.
- Cosmetic surfaces face up or sideways, the bottom face takes on the bed texture and the top face is the smoothest.
Infill, the other half of strength
Above ~30% infill, returns diminish quickly: doubling infill from 30% to 60% only adds about 25% strength, but adds nearly 80% to print time and material cost. For most parts, 20-30% gyroid is the sweet spot.
For high-load parts, increase wall count (3-5 perimeters) before raising infill , perimeters carry far more load per gram than infill does.
Tell us the load case
If we know which way the part will be loaded, we'll orient it for you at slice time. Drop a note in checkout, “mounting bolts go through the long axis, load is vertical” is enough.
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Last reviewed May 2026 · Rigid Prints engineering team