Plastic PMMA vs. Stainless Steel 303

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

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Plastic PMMABulk 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	80MPasourcetypical, 23 °C	585MPasourceOutokumpu typical
Compressive strength	110MPasourcecompressive yield stress, typical	not sourced
Flexural strength	115MPasourcetypical	not sourced
Elongation at break	5.5%sourcetypical	35%sourceOutokumpu typical, A5
Young's modulus (stiffness)	3.3GPasourcetypical, short-term	200GPasourceat RT (Table 12)
Density	1,190kg/m³sourcetypical	7,900kg/m³sourceat RT
Strength to weight	67.2kN·m/kg1.93x higher	34.8kN·m/kg
Stiffness to weight	2.77MN·m/kg	25.3MN·m/kg9.13x higher
Poisson's ratio	0.37sourcetypical	0.3sourcedesign value (structural stainless steels)
Shear modulus	1.2GPa	76.9GPa63.9x stiffer in shear
Bulk modulus	4.23GPa	167GPa
Speed of sound	1,665m/s	5,032m/s
Thermal
Thermal conductivity	0.19W/m·Ksourcetypical	15W/m·Ksourceat RT
Thermal expansion	70µm/m·Ksource0-50 °C	16µm/m·Ksourcemean, 20–100 °C
100 mm part over a 50 °C swing	350µm growth	80µm growth4.38x less
Specific heat	1,470J/kg·Ksourcetypical	500J/kg·Ksourceat RT
Heats up and cools (diffusivity)	0.109mm²/s	3.8mm²/s35x faster
Thermal shock resistance	41.5W/m	902W/m21.8x more resistant
Max service temperature	80°Csourcemax. permanent service temperature	871°Csourcecontinuous, scaling limit
Values for	Röhm PLEXIGLAS GS 0F00 cast acrylic sheet, typical values at 23 °C / 50 % RH (Röhm Technical Information Ref. No. 211-1)	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 PMMA stronger than Stainless Steel 303?

Stainless Steel 303 is stronger: its yield strength is 275 MPa against tensile strength 80 MPa for Plastic PMMA (3.44x).

Which is lighter, Plastic PMMA or Stainless Steel 303?

Plastic PMMA is lighter: 1,190 kg/m³ against 7,900 kg/m³ for Stainless Steel 303.

Which is stiffer, Plastic PMMA or Stainless Steel 303?

Stainless Steel 303 is stiffer: Young's modulus 200 GPa against 3.3 GPa for Plastic PMMA, so the same part in Stainless Steel 303 deflects less under the same load.

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

For the same stiffness or strength: Plastic PMMA is lighter for a 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), stiff beam (bending).

Part that must be	Plastic PMMA	Stainless Steel 303
Stiff rod or tie (tension)	9.13x heavier	lighter
Stiff beam (bending)	17% heavier	lighter
Stiff panel or plate	lighter	1.69x heavier
Strong rod or tie	lighter	1.93x heavier
Strong beam	lighter	2.91x heavier
Strong panel or plate	lighter	3.58x 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 PMMA or Stainless Steel 303?

Stainless Steel 303 conducts heat better: 15 W/m·K against 0.19 W/m·K for Plastic PMMA.

Which expands less with temperature?

Stainless Steel 303 expands less: 16 µm/m·K against 70 µm/m·K for Plastic PMMA.

Among 72 materials

Stiffness against density

Strength against density