Plastic PBT GF30 vs. Stainless Steel 303

Compare Plastic PBT GF30 vs. Stainless Steel 303 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)	275MPasourceOutokumpu typical (product P = hot rolled plate, transverse)
Ultimate tensile strength	140MPasourcestress at break, 23 °C	585MPasourceOutokumpu typical
Flexural strength	210MPasourcetypical, 23 °C	not sourced
Elongation at break	3%sourcestrain at break, 23 °C	35%sourceOutokumpu typical, A5
Young's modulus (stiffness)	9.8GPasourcetypical, 23 °C	200GPasourceat RT (Table 12)
Density	1,530kg/m³sourcetypical	7,900kg/m³sourceat RT
Strength to weight	91.5kN·m/kg2.63x higher	34.8kN·m/kg
Stiffness to weight	6.41MN·m/kg	25.3MN·m/kg3.95x higher
Poisson's ratio	not sourced	0.3sourcedesign value (structural stainless steels)
Shear modulus	not sourced	76.9GPa
Bulk modulus	not sourced	167GPa
Speed of sound	2,531m/s	5,032m/s
Thermal
Thermal conductivity	0.27W/m·Ksourcetypical (DIN 52612-1)	15W/m·Ksourceat RT
Thermal expansion	25µm/m·Ksourcelongitudinal (flow), mean 23-55 °C	16µm/m·Ksourcemean, 20–100 °C
100 mm part over a 50 °C swing	125µm growth	80µm growth1.56x less
Specific heat	1,050J/kg·Ksourcetypical, 23 °C	500J/kg·Ksourceat RT
Heats up and cools (diffusivity)	0.168mm²/s	3.8mm²/s22.6x faster
Thermal shock resistance	not sourced	902W/m
Melting point	223°CsourceDSC (ISO 11357)	not sourced
Max service temperature	205°CsourceHDT 1.8 MPa	871°Csourcecontinuous, scaling limit
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.	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 PBT GF30 stronger than Stainless Steel 303?

Stainless Steel 303 is stronger: its yield strength is 275 MPa against tensile strength 140 MPa for Plastic PBT GF30 (1.96x).

Which is lighter, Plastic PBT GF30 or Stainless Steel 303?

Plastic PBT GF30 is lighter: 1,530 kg/m³ against 7,900 kg/m³ for Stainless Steel 303.

Which is stiffer, Plastic PBT GF30 or Stainless Steel 303?

Stainless Steel 303 is stiffer: Young's modulus 200 GPa against 9.8 GPa for Plastic PBT GF30, so the same part in Stainless Steel 303 deflects less under the same load.

Which is lighter for the same job, Plastic PBT GF30 or Stainless Steel 303?

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 303 is lighter for a stiff rod or tie (tension).

Part that must be	Plastic PBT GF30	Stainless Steel 303
Stiff rod or tie (tension)	3.95x heavier	lighter
Stiff beam (bending)	lighter	14% heavier
Stiff panel or plate	lighter	1.89x heavier
Strong rod or tie	lighter	2.63x heavier
Strong beam	lighter	3.29x heavier
Strong panel or plate	lighter	3.68x 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 303?

Stainless Steel 303 conducts heat better: 15 W/m·K against 0.27 W/m·K for Plastic PBT GF30.

Which expands less with temperature?

Stainless Steel 303 expands less: 16 µm/m·K against 25 µm/m·K for Plastic PBT GF30.

Among 72 materials

Stiffness against density

Strength against density