Plastic HDPE vs. Stainless Steel 303

Compare Plastic HDPE vs. Stainless Steel 303 strength, stiffness, weight and thermal properties.

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Plastic HDPEBulk polymer (molded or machined)

Mechanical
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Yield strength	24MPasourcetypical, tensile stress at yield 23 °C, 50 mm/min ISO 527	275MPasourceOutokumpu typical (product P = hot rolled plate, transverse)
Ultimate tensile strength	not sourced	585MPasourceOutokumpu typical
Elongation at break	not sourced	35%sourceOutokumpu typical, A5
Young's modulus (stiffness)	0.9GPasourcetypical, tensile modulus 23 °C ISO 527	200GPasourceat RT (Table 12)
Density	950kg/m³sourcetypical, ISO 1183	7,900kg/m³sourceat RT
Strength to weight	25.3kN·m/kg	34.8kN·m/kg38% higher
Stiffness to weight	0.947MN·m/kg	25.3MN·m/kg26.7x higher
Poisson's ratio	0.4–0.45sourcebase material: high-density polyethylene family (INEOS Olefins & Polymers USA, Typical Engineering Properties of HDPE)	0.3sourcedesign value (structural stainless steels)
Shear modulus	0.316GPa	76.9GPa244x stiffer in shear
Bulk modulus	2GPa	167GPa
Speed of sound	973m/s	5,032m/s
Thermal
Thermal conductivity	0.4–0.49W/m·Ksourcebase material: high-density polyethylene family (INEOS Olefins & Polymers USA, Typical Engineering Properties of HDPE)	15W/m·Ksourceat RT
Thermal expansion	120µm/m·Ksourcebase material: high-density polyethylene family (INEOS Olefins & Polymers USA, Typical Engineering Properties of HDPE)	16µm/m·Ksourcemean, 20–100 °C
100 mm part over a 50 °C swing	600µm growth	80µm growth7.5x less
Specific heat	2,250J/kg·Ksourcebase material: high-density polyethylene family (INEOS Olefins & Polymers USA, Typical Engineering Properties of HDPE)	500J/kg·Ksourceat RT
Heats up and cools (diffusivity)	0.208mm²/s	3.8mm²/s18.2x faster
Thermal shock resistance	56.9W/m	902W/m15.9x more resistant
Max service temperature	not sourced	871°Csourcecontinuous, scaling limit
Values for	LyondellBasell Hostalen 23050 B high density polyethylene, typical ISO values	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 HDPE stronger than Stainless Steel 303?

Stainless Steel 303 is stronger: its yield strength is 275 MPa against 24 MPa for Plastic HDPE (11.5x).

Which is lighter, Plastic HDPE or Stainless Steel 303?

Plastic HDPE is lighter: 950 kg/m³ against 7,900 kg/m³ for Stainless Steel 303.

Which is stiffer, Plastic HDPE or Stainless Steel 303?

Stainless Steel 303 is stiffer: Young's modulus 200 GPa against 0.9 GPa for Plastic HDPE, so the same part in Stainless Steel 303 deflects less under the same load.

Which is lighter for the same job, Plastic HDPE or Stainless Steel 303?

For the same stiffness or strength: Plastic HDPE is lighter for a stiff panel or plate, strong beam, strong panel or plate; Stainless Steel 303 is lighter for a stiff rod or tie (tension), stiff beam (bending), strong rod or tie.

Part that must be	Plastic HDPE	Stainless Steel 303
Stiff rod or tie (tension)	26.7x heavier	lighter
Stiff beam (bending)	1.79x heavier	lighter
Stiff panel or plate	lighter	37% heavier
Strong rod or tie	38% heavier	lighter
Strong beam	lighter	1.64x heavier
Strong panel or plate	lighter	2.46x 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 HDPE or Stainless Steel 303?

Stainless Steel 303 conducts heat better: 15 W/m·K against 0.445 W/m·K for Plastic HDPE.

Which expands less with temperature?

Stainless Steel 303 expands less: 16 µm/m·K against 120 µm/m·K for Plastic HDPE.

Among 72 materials

Stiffness against density

Strength against density