Plastic HDPE vs. Plastic Polycarbonate

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

Plastic HDPEBulk polymer (molded or machined)

Plastic PolycarbonateBulk polymer (molded or machined)

Mechanical	Plastic HDPE	Plastic Polycarbonate
Yield strength	24MPa1	65MPa22.71x stronger
Ultimate tensile strength	not stated (yield given)	65MPa2
Flexural strength	not sourced	97MPa2
Elongation at break	not sourced	125%2
Young's modulus (stiffness)	0.9GPa1	2.4GPa22.67x stiffer
Density	950kg/m³126% lighter	1,200kg/m³2
Strength to weight	25.3kN·m/kg	54.2kN·m/kg2.14x higher
Stiffness to weight	0.947MN·m/kg	2MN·m/kg2.11x higher
Poisson's ratio	base material0.4–0.453	0.384
Shear modulus	0.316GPa	0.87GPa2.75x stiffer in shear
Bulk modulus	2GPa	3.33GPa1.67x higher
Speed of sound	973m/s	1,414m/s45% 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 Polycarbonate
Thermal conductivity	base material0.4–0.49W/m·K3	0.2W/m·K2
Thermal expansion	base material120µm/m·K3	65µm/m·K21.85x less
100 mm part over a 50 °C swing	600µm growth	325µm growth1.85x less
Specific heat	base material2,250J/kg·K31.92x higher	1,172J/kg·K5
Heats up and cools (diffusivity)	0.208mm²/s46% faster	0.142mm²/s
Thermal shock resistance	56.9W/m10% more resistant	51.7W/m
Glass transition	not sourced	144°C2
Max service temperature	not sourced	UL 746B RTI125°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

Sources5 documents: LyondellBasell, Covestro, INEOS Olefins & Polymers USA, Bayer MaterialScience

Plastic HDPE: LyondellBasell Hostalen 23050 B high density polyethylene, typical ISO values
Plastic Polycarbonate: Covestro Makrolon 2405 general-purpose PC (MVR 19), Covestro technical datasheet version 2026-09-28, typical 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
Makrolon 2405 Technical Data SheetCovestroPlastic Polycarbonate · Yield strength: typical, tensile yieldPlastic Polycarbonate · Ultimate tensile strength: typical, stress at breakPlastic Polycarbonate · Flexural strength: typical, flexural strengthPlastic Polycarbonate · Elongation at break: typical, strain at breakPlastic Polycarbonate · Young's modulus (stiffness): typicalPlastic Polycarbonate · Density: typicalPlastic Polycarbonate · Thermal conductivity: typical, through-plane, 23 CPlastic Polycarbonate · Thermal expansion: typical, 23-55 C, parallel and normalPlastic Polycarbonate · Glass transition: typical, DSC 10 C/minPlastic Polycarbonate · Max service temperature: UL 746B RTI, tensile strength, 1.5 mm
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
Engineering Polymers Part and Mold Design: Thermoplastics, A Design GuideCovestroarchived copyPlastic Polycarbonate · Poisson's ratio: typical, polycarbonate family (Covestro Part and Mold Design guide, Table 3-1)
5
Makrolon 2405 Data Sheet, ASTM valuesBayer MaterialSciencearchived copyPlastic Polycarbonate · Specific heat: typical (guide value), Bayer ASTM datasheet for Makrolon 2405, ASTM D 2766

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 Polycarbonate?

Plastic Polycarbonate is stronger: its yield strength is 65 MPa against 24 MPa for Plastic HDPE (2.71x).

Which is lighter, Plastic HDPE or Plastic Polycarbonate?

Plastic HDPE is lighter: 950 kg/m³ against 1,200 kg/m³ for Plastic Polycarbonate.

Which is stiffer, Plastic HDPE or Plastic Polycarbonate?

Plastic Polycarbonate is stiffer: Young's modulus 2.4 GPa against 0.9 GPa for Plastic HDPE, so the same part in Plastic Polycarbonate deflects less under the same load.

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

For the same stiffness or strength: Plastic Polycarbonate 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 Polycarbonate
Stiff rod or tie (tension)	2.11x heavier	lighter
Stiff beam (bending)	29% heavier	lighter
Stiff panel or plate	10% heavier	lighter
Strong rod or tie	2.14x heavier	lighter
Strong beam	1.54x heavier	lighter
Strong panel or plate	30% 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 Polycarbonate?

Plastic HDPE conducts heat better: 0.445 W/m·K against 0.2 W/m·K for Plastic Polycarbonate.

Which expands less with temperature?

Plastic Polycarbonate expands less: 65 µm/m·K against 120 µm/m·K for Plastic HDPE.