- Tensile strength
- How much pulling force the printed material takes before it snaps, measured along the print plane (the strong direction). The headline strength number. Strength between layers (Z-axis) is always lower for 3D-printed parts.
- Heat ceiling (HDT)
- The temperature where the material starts to lose shape under load — the real-world heat ceiling, not the print temperature. Day-to-day service is usually 20–50°C below this number.
- Young's modulus (stiffness)
- Resistance to elastic deformation. High modulus = rigid (carbon/glass composites); low modulus = compliant. Distinct from strength · a material can be strong but flexible, or stiff but brittle.
- Notched Charpy impact
- Energy absorbed before fracture from a notched specimen (ISO 179). Low = brittle (clean snap), high = tough (absorbs impact). Composites can be low on this lab test yet strong in real structural use.
- Anisotropy
- FDM parts are stronger along layers than across them. Orientation at print time changes the result · part design and print orientation are tuned per job.
- Datasheet vs real-world
- TDS values are from injection-moulded ISO bars, not FDM prints. We cite them as the baseline but qualify every recommendation with how the grade actually prints · the practitioner layer.
- Annealing
- Post-print heat treatment that raises crystallinity/HDT (semi-crystalline grades · PPS, PET, PA family) or relieves print stress. Some grades require it to reach rated performance; PLA cannot usefully be annealed.