Ranked on tensile strength alone, the selector returns PPA first at 90 to 150 MPa, then PA6-CF at 80 to 130, PEEK at 90 to 110, PA6-GF at 70 to 110 and ULTEM 9085 at 69 to 76.
None of those is a realistic answer for most people, which is the interesting part.
Strongest at what?
Tensile strength is one number and it is rarely the one that matters.
- Stiffness — how much a part deflects under load before it fails. The fibre-filled grades win here far more decisively than the tensile figures suggest.
- Impact resistance — how much energy a part absorbs before cracking. Unfilled nylon and PC beat every filled grade, which are stiff but brittle.
- Layer adhesion — how strong the part is in the direction it will actually break. This is a printing property, not a material one, and it dominates real failures.
A part that snaps along a layer line failed at a weld, not at the polymer. Print orientation and nozzle temperature control that, and they will outweigh any material choice made on a data sheet.
What your printer can actually run
PPA needs 290 to 320 °C and a heated chamber. PEEK needs 380 to 440 °C. ULTEM needs 350 to 390 °C with a 140 to 160 °C bed.
Ask the same question with a realistic machine — an enclosed printer with a 300 °C hotend — and PEEK and ULTEM are ruled out entirely, leaving PPA, PA6-CF, PC-ABS and PA6-GF.
The strongest filament you can probably print
PA6-CF, at 80 to 130 MPa, with a heat deflection band of 120 to 190 °C. It needs an enclosure, a hardened nozzle, and 8 to 12 hours of drying at 80 °C before every session — and it costs $60 to $120 a kilogram.
If that is more machine than you have, unfilled PA6 at 50 to 80 MPa is genuinely tough and far more forgiving. PETG at 45 to 55 MPa beats PLA on toughness while printing on anything.
Rank materials against your own requirements and machine limits in the material selector.