Plastic PBT GF30 vs. Stainless Steel 304

Compare Plastic PBT GF30 vs. Stainless Steel 304 strength, stiffness, weight and thermal properties.

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Plastic PBT GF30Bulk polymer (molded or machined)

Mechanical
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Yield strength	not given (tensile used)	241MPasourcetypical, annealed, 70 °F (21 °C)
Ultimate tensile strength	140MPasourcestress at break, 23 °C	586MPasourcetypical, annealed, 70 °F (21 °C)
Flexural strength	210MPasourcetypical, 23 °C	not sourced
Elongation at break	3%sourcestrain at break, 23 °C	55%sourcetypical, annealed, in 2 in. (50.8 mm)
Young's modulus (stiffness)	9.8GPasourcetypical, 23 °C	193GPasourcetypical, in tension
Density	1,530kg/m³sourcetypical5.25x lighter	8,030kg/m³sourcetypical
Strength to weight	91.5kN·m/kg3.05x higher	30kN·m/kg
Stiffness to weight	6.41MN·m/kg	24MN·m/kg3.75x higher
Poisson's ratio	not sourced	0.3sourcedesign value (structural stainless steels)
Shear modulus	not sourced	74.2GPa
Bulk modulus	not sourced	161GPa
Speed of sound	2,531m/s	4,903m/s
Thermal
Thermal conductivity	0.27W/m·Ksourcetypical (DIN 52612-1)	16.2W/m·Ksourceat 100 °C
Thermal expansion	25µm/m·Ksourcelongitudinal (flow), mean 23-55 °C	16.9µm/m·Ksourcemean, 0–100 °C
100 mm part over a 50 °C swing	125µm growth	84.5µm growth48% less
Specific heat	1,050J/kg·Ksourcetypical, 23 °C	500J/kg·Ksourcemean, 0–100 °C
Heats up and cools (diffusivity)	0.168mm²/s	4.03mm²/s24x faster
Thermal shock resistance	not sourced	838W/m
Melting point	223°CsourceDSC (ISO 11357)	1,399–1,454°Csourcemelting range
Max service temperature	205°CsourceHDT 1.8 MPa	899°Csourcecontinuous, oxidation (scaling) limit in air
Values for	BASF Ultradur B 4300 G6 (PBT, 30% glass fibre), injection moulding grade; product information sheet 09/2026, typical values for uncoloured product at 23 °C.	Type 304, annealed flat-rolled (Cleveland-Cliffs 304/304L Product Data Bulletin, May 2021); Poisson's ratio from the Nickel Institute/SCI structural stainless design manual

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 PBT GF30 stronger than Stainless Steel 304?

Stainless Steel 304 is stronger: its yield strength is 241 MPa against tensile strength 140 MPa for Plastic PBT GF30 (1.72x).

Which is lighter, Plastic PBT GF30 or Stainless Steel 304?

Plastic PBT GF30 is lighter: 1,530 kg/m³ against 8,030 kg/m³ for Stainless Steel 304.

Which is stiffer, Plastic PBT GF30 or Stainless Steel 304?

Stainless Steel 304 is stiffer: Young's modulus 193 GPa against 9.8 GPa for Plastic PBT GF30, so the same part in Stainless Steel 304 deflects less under the same load.

Which is lighter for the same job, Plastic PBT GF30 or Stainless Steel 304?

For the same stiffness or strength: Plastic PBT GF30 is lighter for a stiff beam (bending), stiff panel or plate, strong rod or tie, strong beam, strong panel or plate; Stainless Steel 304 is lighter for a stiff rod or tie (tension).

Part that must be	Plastic PBT GF30	Stainless Steel 304
Stiff rod or tie (tension)	3.75x heavier	lighter
Stiff beam (bending)	lighter	18% heavier
Stiff panel or plate	lighter	1.94x heavier
Strong rod or tie	lighter	3.05x heavier
Strong beam	lighter	3.65x heavier
Strong panel or plate	lighter	4x 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 PBT GF30 or Stainless Steel 304?

Stainless Steel 304 conducts heat better: 16.2 W/m·K against 0.27 W/m·K for Plastic PBT GF30.

Which expands less with temperature?

Stainless Steel 304 expands less: 16.9 µm/m·K against 25 µm/m·K for Plastic PBT GF30.

Among 72 materials

Stiffness against density

Strength against density