Materials / Compare
Plastic PEEK vs. Stainless 303
Compare Plastic PEEK vs. Stainless 303 strength, stiffness, weight and thermal properties.
| Try it on a partA bracket to run stress or thermal on, free in your browser | Open in LessCAD | Open in LessCAD |
|---|---|---|
| Mechanical | ||
| Yield strength | 98MPasourcetypical, tensile yield | 275MPasourceOutokumpu typical (product P = hot rolled plate, transverse) |
| Ultimate tensile strength | not sourced | 585MPasourceOutokumpu typical |
| Compressive strength | 125MPasourcetypical, 23 C | not sourced |
| Flexural strength | 165MPasourcetypical, flexural stress at yield, 23 C | not sourced |
| Elongation at break | 25%sourcetypical, at break | 35%sourceOutokumpu typical, A5 |
| Young's modulus (stiffness) | 4GPasourcetypical (nominal) | 200GPasourceat RT (Table 12) |
| Density | 1,300kg/m³sourcetypical (crystalline) | 7,900kg/m³sourceat RT |
| Strength to weight | 75.4kN·m/kg2.17x higher | 34.8kN·m/kg |
| Stiffness to weight | 3.08MN·m/kg | 25.3MN·m/kg8.23x higher |
| Poisson's ratio | 0.38sourcetypical | 0.3sourcedesign value (structural stainless steels) |
| Shear modulus | 1.45GPa | 76.9GPa53.1x stiffer in shear |
| Bulk modulus | 5.56GPa | 167GPa |
| Speed of sound | 1,754m/s | 5,032m/s |
| Thermal | ||
| Thermal conductivity | 0.29W/m·Ksourcetypical, average, 23 C | 15W/m·Ksourceat RT |
| Thermal expansion | 55µm/m·Ksourceaverage of flow/cross-flow, below Tg (<143 C) | 16µm/m·Ksourcemean, 20–100 °C |
| 100 mm part over a 50 °C swing | 275µm growth | 80µm growth3.44x less |
| Specific heat | 2,200J/kg·Ksourcetypical, 23 °C, DSC (Victrex PEEK 450G TDS, revision Jul 2012) | 500J/kg·Ksourceat RT |
| Heats up and cools (diffusivity) | 0.101mm²/s | 3.8mm²/s37.5x faster |
| Thermal shock resistance | 80.1W/m | 902W/m11.3x more resistant |
| Melting point | 343°Csourcetypical, DSC | not sourced |
| Glass transition | 143°Csourceonset (midpoint 150 C) | not sourced |
| Max service temperature | 240°CsourceUL 746B RTI, mechanical strength (continuous use index) | 871°Csourcecontinuous, scaling limit |
| Values for | Victrex PEEK 450G (unreinforced, injection moulded), Victrex TDS rev. March 2026; Poisson from Victrex fluid-management flyer (2020-07) | 1.4305 / UNS S30300, Outokumpu typical values (hot rolled, solution annealed) from 'Steel Grades, Properties and Global Standards'; max service from Carpenter CarTech 303 datasheet |
Every value links to the document that states it. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.
Questions
Is Plastic PEEK stronger than Stainless 303?
Stainless 303 is stronger: its yield strength is 275 MPa against 98 MPa for Plastic PEEK (2.81x).
Which is lighter, Plastic PEEK or Stainless 303?
Plastic PEEK is lighter: 1,300 kg/m³ against 7,900 kg/m³ for Stainless 303.
Which is stiffer, Plastic PEEK or Stainless 303?
Stainless 303 is stiffer: Young's modulus 200 GPa against 4 GPa for Plastic PEEK, so the same part in Stainless 303 deflects less under the same load.
Which is lighter for the same job, Plastic PEEK or Stainless 303?
For the same stiffness or strength: Plastic PEEK is lighter for a stiff panel or plate, strong rod or tie, strong beam, strong panel or plate; Stainless 303 is lighter for a stiff rod or tie (tension), stiff beam (bending).
| Part that must be | Plastic PEEK | Stainless 303 |
|---|---|---|
| Stiff rod or tie (tension) | 8.23x heavier | lighter |
| Stiff beam (bending) | 16% heavier | lighter |
| Stiff panel or plate | lighter | 1.65x heavier |
| Strong rod or tie | lighter | 2.17x heavier |
| Strong beam | lighter | 3.05x heavier |
| Strong panel or plate | lighter | 3.63x heavier |
For the same stiffness or strength, mass scales with density over stiffness (or strength) raised to a power set by how the part is loaded: 1 for a rod in tension, 1/2 for a beam in bending, 1/3 for a panel (the standard material-selection indices).
Which conducts heat better, Plastic PEEK or Stainless 303?
Stainless 303 conducts heat better: 15 W/m·K against 0.29 W/m·K for Plastic PEEK.
Which expands less with temperature?
Stainless 303 expands less: 16 µm/m·K against 55 µm/m·K for Plastic PEEK.