Materials / Compare
Plastic PEEK vs. Steel
Compare Plastic PEEK vs. Steel 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 | 385MPasourcetypical: mean of 20,295 A992 flange mill-test coupons (1998 SSPC survey), as reported by AISC |
| Ultimate tensile strength | not sourced | 505MPasourcetypical: mean of 20,295 A992 flange mill-test coupons (1998 SSPC survey) |
| 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 | not sourced |
| Young's modulus (stiffness) | 4GPasourcetypical (nominal) | 200GPasourcedesign value (AISC 360-16) |
| Density | 1,300kg/m³sourcetypical (crystalline) | 7,850kg/m³sourcenominal (constructional data) |
| Strength to weight | 75.4kN·m/kg1.54x higher | 49kN·m/kg |
| Stiffness to weight | 3.08MN·m/kg | 25.5MN·m/kg8.28x higher |
| Poisson's ratio | 0.38sourcetypical | 0.3sourcedesign value (AISC 360-16 Commentary) |
| Shear modulus | 1.45GPa | 76.9GPa53.1x stiffer in shear |
| Bulk modulus | 5.56GPa | 167GPa |
| Speed of sound | 1,754m/s | 5,048m/s |
| Thermal | ||
| Thermal conductivity | 0.29W/m·Ksourcetypical, average, 23 C | 48W/m·Ksourcenominal at 20 °C |
| Thermal expansion | 55µm/m·Ksourceaverage of flow/cross-flow, below Tg (<143 C) | 12µm/m·Ksourcenominal (constructional data, no temperature range stated) |
| 100 mm part over a 50 °C swing | 275µm growth | 60µm growth4.58x less |
| Specific heat | 2,200J/kg·Ksourcetypical, 23 °C, DSC (Victrex PEEK 450G TDS, revision Jul 2012) | 460–480J/kg·Ksourcebase material: EN S275JR unalloyed structural steel (the EN counterpart of A36), typical, 50/100 °C |
| Heats up and cools (diffusivity) | 0.101mm²/s | 13mm²/s128x faster |
| Thermal shock resistance | 80.1W/m | 5,390W/m67.3x 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) | not sourced |
| Values for | Victrex PEEK 450G (unreinforced, injection moulded), Victrex TDS rev. March 2026; Poisson from Victrex fluid-management flyer (2020-07) | Generic structural steel, cited as ASTM A992 (the current US structural grade): ASTM A992 W-shapes; Fy/Fu specified minimums from AISC publications (AISC 360-16 Commentary; Modern Steel Construction); elastic constants AISC 360; physical constants from the bauforumstahl structural-steel EPD, which names A992 among covered product standards. |
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 Steel?
Steel is stronger: its yield strength is 385 MPa against 98 MPa for Plastic PEEK (3.93x).
Which is lighter, Plastic PEEK or Steel?
Plastic PEEK is lighter: 1,300 kg/m³ against 7,850 kg/m³ for Steel.
Which is stiffer, Plastic PEEK or Steel?
Steel is stiffer: Young's modulus 200 GPa against 4 GPa for Plastic PEEK, so the same part in Steel deflects less under the same load.
Which is lighter for the same job, Plastic PEEK or Steel?
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; Steel is lighter for a stiff rod or tie (tension), stiff beam (bending).
| Part that must be | Plastic PEEK | Steel |
|---|---|---|
| Stiff rod or tie (tension) | 8.28x heavier | lighter |
| Stiff beam (bending) | 17% heavier | lighter |
| Stiff panel or plate | lighter | 1.64x heavier |
| Strong rod or tie | lighter | 1.54x heavier |
| Strong beam | lighter | 2.43x heavier |
| Strong panel or plate | lighter | 3.05x 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 Steel?
Steel conducts heat better: 48 W/m·K against 0.29 W/m·K for Plastic PEEK.
Which expands less with temperature?
Steel expands less: 12 µm/m·K against 55 µm/m·K for Plastic PEEK.