Thermal conductivity against densityHigher and further left: spreads more heat for its weightThermal expansion against thermal conductivityLower and further right: warps less when heated
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Sources5 documents: Victrex, LyondellBasell, INEOS Olefins & Polymers USA
Plastic PEEK
Victrex PEEK 450G (unreinforced, injection moulded), Victrex TDS rev. March 2026; Poisson from Victrex fluid-management flyer (2020-07)
Plastic Polypropylene
LyondellBasell Moplen HP501H polypropylene homopolymer (general purpose), typical ISO values
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VICTREX PEEK 450G Technical Data SheetVictrexPlastic PEEK · Yield strength: typical, tensile yieldPlastic PEEK · Compressive strength: typical, 23 CPlastic PEEK · Flexural strength: typical, flexural stress at yield, 23 CPlastic PEEK · Elongation at break: typical, at breakPlastic PEEK · Young's modulus (stiffness): typical (nominal)Plastic PEEK · Density: typical (crystalline)Plastic PEEK · Thermal conductivity: typical, average, 23 CPlastic PEEK · Thermal expansion: average of flow/cross-flow, below Tg (<143 C)Plastic PEEK · Melting point: typical, DSCPlastic PEEK · Glass transition: onset (midpoint 150 C)Plastic PEEK · Max service temperature: UL 746B RTI, mechanical strength (continuous use index)
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Moplen HP501H Product DataLyondellBasellPlastic Polypropylene · Yield strength: typical, tensile stress at yield ISO 527Plastic Polypropylene · Young's modulus (stiffness): typical, tensile modulus ISO 527Plastic Polypropylene · Density: typical, 23 °C ISO 1183-1Plastic Polypropylene · Max service temperature: HDT 0.45 MPa (ISO 75B), unannealed
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VICTREX PEEK for Use in Fluid Management (2020)VictrexPlastic PEEK · Poisson's ratio: typical
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Typical Engineering Properties of PolypropyleneINEOS Olefins & Polymers USAarchived copyPlastic Polypropylene · Poisson's ratio: base material: polypropylene homopolymer family (INEOS Olefins & Polymers USA, Typical Engineering Properties of Polypropylene)Plastic Polypropylene · Thermal conductivity: base material: polypropylene homopolymer family (INEOS Olefins & Polymers USA, Typical Engineering Properties of Polypropylene)Plastic Polypropylene · Thermal expansion: base material: polypropylene homopolymer family (INEOS Olefins & Polymers USA, Typical Engineering Properties of Polypropylene)
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VICTREX PEEK 450G Technical Data Sheet (2012)Victrexarchived copyPlastic PEEK · Specific heat: typical, 23 °C, DSC (Victrex PEEK 450G TDS, revision Jul 2012)
Each number points to the document that states it, with the exact basis. Values without a number are computed from the sourced ones. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.
Questions
Mechanical
Is Plastic PEEK stronger than Plastic Polypropylene?
Plastic PEEK is stronger: its yield strength is 98 MPa against 33 MPa for Plastic Polypropylene (2.97x).
Which is lighter, Plastic PEEK or Plastic Polypropylene?
Plastic Polypropylene is lighter: 900 kg/m³ against 1,300 kg/m³ for Plastic PEEK.
Which is stiffer, Plastic PEEK or Plastic Polypropylene?
Plastic PEEK is stiffer: Young's modulus 4 GPa against 1.45 GPa for Plastic Polypropylene, so the same part in Plastic PEEK deflects less under the same load.
Which is lighter for the same job, Plastic PEEK or Plastic Polypropylene?
For the same stiffness or strength: Plastic PEEK is lighter for a stiff rod or tie (tension), stiff beam (bending), strong rod or tie, strong beam, strong panel or plate; Plastic Polypropylene is lighter for a stiff panel or plate.
Part that must be
Plastic PEEK
Plastic Polypropylene
Stiff rod or tie (tension)
lighter
1.91x heavier
Stiff beam (bending)
lighter
15% heavier
Stiff panel or plate
3% heavier
lighter
Strong rod or tie
lighter
2.06x heavier
Strong beam
lighter
43% heavier
Strong panel or plate
lighter
19% 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).
Thermal
Which conducts heat better, Plastic PEEK or Plastic Polypropylene?
Plastic PEEK conducts heat better: 0.29 W/m·K against 0.195 W/m·K for Plastic Polypropylene.
Which expands less with temperature?
Plastic PEEK expands less: 55 µm/m·K against 90 µm/m·K for Plastic Polypropylene.