Plastic HDPE vs. Plastic Polypropylene

Compare Plastic HDPE vs. Plastic Polypropylene strength, stiffness, weight and thermal properties.

Plastic HDPEBulk polymer (molded or machined)

Plastic PolypropyleneBulk polymer (molded or machined)

Mechanical	Plastic HDPE	Plastic Polypropylene
Yield strength	24MPa1	33MPa238% stronger
Ultimate tensile strength	not stated (yield given)	not stated (yield given)
Elongation at break	not sourced	not sourced
Young's modulus (stiffness)	0.9GPa1	1.45GPa21.61x stiffer
Density	950kg/m³1	900kg/m³2
Strength to weight	25.3kN·m/kg	36.7kN·m/kg45% higher
Stiffness to weight	0.947MN·m/kg	1.61MN·m/kg1.7x higher
Poisson's ratio	base material0.4–0.453	base material0.424
Shear modulus	0.316GPa	0.511GPa1.62x stiffer in shear
Bulk modulus	2GPa	3.02GPa1.51x higher
Speed of sound	973m/s	1,269m/s30% faster

Stiffness against densityHigher and further left: stiffer for its weight

Strength against densityHigher and further left: stronger for its weight

Thermal	Plastic HDPE	Plastic Polypropylene
Thermal conductivity	base material0.4–0.49W/m·K3	base material0.17–0.22W/m·K4
Thermal expansion	base material120µm/m·K3	base material80–100µm/m·K4
100 mm part over a 50 °C swing	600µm growth	450µm growth33% less
Specific heat	base material2,250J/kg·K3	not sourced
Heats up and cools (diffusivity)	0.208mm²/s	not sourced
Thermal shock resistance	56.9W/m1.99x more resistant	28.6W/m
Max service temperature	not sourced	HDT 0.45 MPa90°C2

Thermal conductivity against densityHigher and further left: spreads more heat for its weight

Thermal expansion against thermal conductivityLower and further right: warps less when heated

Try it on a partA bracket to run stress or thermal on, free in your browser	Open in LessCAD	Open in LessCAD

Sources4 documents: LyondellBasell, INEOS Olefins & Polymers USA

Plastic HDPE: LyondellBasell Hostalen 23050 B high density polyethylene, typical ISO values
Plastic Polypropylene: LyondellBasell Moplen HP501H polypropylene homopolymer (general purpose), typical ISO values

1
Hostalen 23050 B Product DataLyondellBasellPlastic HDPE · Yield strength: typical, tensile stress at yield 23 °C, 50 mm/min ISO 527Plastic HDPE · Young's modulus (stiffness): typical, tensile modulus 23 °C ISO 527Plastic HDPE · Density: typical, ISO 1183
2
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
3
Typical Engineering Properties of High Density PolyethyleneINEOS Olefins & Polymers USAarchived copyPlastic HDPE · Poisson's ratio: base material: high-density polyethylene family (INEOS Olefins & Polymers USA, Typical Engineering Properties of HDPE)Plastic HDPE · Thermal conductivity: base material: high-density polyethylene family (INEOS Olefins & Polymers USA, Typical Engineering Properties of HDPE)Plastic HDPE · Thermal expansion: base material: high-density polyethylene family (INEOS Olefins & Polymers USA, Typical Engineering Properties of HDPE)Plastic HDPE · Specific heat: base material: high-density polyethylene family (INEOS Olefins & Polymers USA, Typical Engineering Properties of HDPE)
4
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)

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 HDPE stronger than Plastic Polypropylene?

Plastic Polypropylene is stronger: its yield strength is 33 MPa against 24 MPa for Plastic HDPE (38%).

Which is lighter, Plastic HDPE or Plastic Polypropylene?

Plastic Polypropylene is lighter: 900 kg/m³ against 950 kg/m³ for Plastic HDPE.

Which is stiffer, Plastic HDPE or Plastic Polypropylene?

Plastic Polypropylene is stiffer: Young's modulus 1.45 GPa against 0.9 GPa for Plastic HDPE, so the same part in Plastic Polypropylene deflects less under the same load.

Which is lighter for the same job, Plastic HDPE or Plastic Polypropylene?

For the same stiffness or strength: Plastic Polypropylene is lighter for a stiff rod or tie (tension), stiff beam (bending), stiff panel or plate, strong rod or tie, strong beam, strong panel or plate.

Part that must be	Plastic HDPE	Plastic Polypropylene
Stiff rod or tie (tension)	1.7x heavier	lighter
Stiff beam (bending)	34% heavier	lighter
Stiff panel or plate	24% heavier	lighter
Strong rod or tie	45% heavier	lighter
Strong beam	31% heavier	lighter
Strong panel or plate	24% heavier	lighter

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 HDPE or Plastic Polypropylene?

Plastic HDPE conducts heat better: 0.445 W/m·K against 0.195 W/m·K for Plastic Polypropylene.

Which expands less with temperature?

Plastic Polypropylene expands less: 90 µm/m·K against 120 µm/m·K for Plastic HDPE.