Plastic POM/Acetal vs. Rubber

Compare Plastic POM/Acetal vs. Rubber strength, stiffness, weight and thermal properties.

Plastic POM/AcetalBulk polymer (molded or machined)

RubberBulk polymer (molded or machined)

Mechanical	Plastic POM/Acetal	Rubber
Yield strength	69MPa1	not given (tensile used)
Ultimate tensile strength	69MPa13x stronger	23MPa2
Compressive strength	124MPa1	not sourced
Flexural strength	99MPa1	not sourced
Elongation at break	75%1	830%211.1x more ductile
Young's modulus (stiffness)	2.8GPa1	not sourced
Density	1,420kg/m³3	960kg/m³248% lighter
Strength to weight	48.6kN·m/kg2.03x higher	24kN·m/kg
Stiffness to weight	1.97MN·m/kg	not sourced
Poisson's ratio	0.351	government0.54
Shear modulus	1.04GPa	not sourced
Bulk modulus	3.11GPa	not sourced
Speed of sound	1,404m/s	not sourced

Stiffness against densityHigher and further left: stiffer for its weight

Strength against densityHigher and further left: stronger for its weight

Thermal	Plastic POM/Acetal	Rubber
Thermal conductivity	0.4W/m·K12.65x more heat through a fin	0.151W/m·K5
Thermal expansion	mean122µm/m·K1	not sourced
100 mm part over a 50 °C swing	610µm growth	not sourced
Specific heat	average -18 to 100 °C1,465J/kg·K1	government1,881J/kg·K428% higher
Heats up and cools (diffusivity)	0.192mm²/s2.3x faster	0.0836mm²/s
Thermal shock resistance	52.5W/m	not sourced
Melting point	175°C1	not sourced
Max service temperature	HDT 1.8 MPa125°C1	70°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

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Sources5 documents: DuPont, Weir Minerals, National Institute of Standards and Technology, Defense Technical Information Center

Plastic POM/Acetal: DuPont Delrin 100 acetal homopolymer, Table 2 'Typical Properties of Delrin Acetal Resins' (ASTM methods), Delrin Design Guide Module III hosted on delrin.com
Rubber: Weir Minerals Linatex Premium rubber (95 % natural rubber), typical physical properties, spec sheet WMD0118/202305

1
Delrin Acetal Resin Design Guide, Module IIIDuPontarchived copyPlastic POM/Acetal · Yield strength: typical (single ASTM D638 tensile strength)Plastic POM/Acetal · Ultimate tensile strength: typicalPlastic POM/Acetal · Compressive strength: compressive stress at 10% deformationPlastic POM/Acetal · Flexural strength: flexural yield strength, typicalPlastic POM/Acetal · Elongation at break: typicalPlastic POM/Acetal · Young's modulus (stiffness): typicalPlastic POM/Acetal · Poisson's ratio: typicalPlastic POM/Acetal · Thermal conductivity: typicalPlastic POM/Acetal · Thermal expansion: mean, 29 to 60 °CPlastic POM/Acetal · Specific heat: average -18 to 100 °C, Delrin acetal resins (not grade-specific)Plastic POM/Acetal · Melting point: crystalline melting pointPlastic POM/Acetal · Max service temperature: HDT 1.8 MPa (annealed)
2
Linatex Premium Rubber Spec Sheet (WMD0118, 2023)Weir MineralsRubber · Ultimate tensile strength: typicalRubber · Elongation at break: typicalRubber · Density: typical (specific gravity)Rubber · Max service temperature: continuous use operating range
3
Delrin 100 Product Data SheetDuPontPlastic POM/Acetal · Density: typical (DuPont product information for Delrin 100 NC010; 'The data listed here fall within the normal range of product properties')
4
Compressibility of Natural Rubber at Pressures Below 500 kg/cm², J. Res. NBS 68A (1964)National Institute of Standards and Technologyarchived copyRubber · Poisson's ratio: government (NBS J. Res. 68A, 1964): computed by NBS for peroxide-cured gum NR vulcanizate, 25 °C, infinitesimal deformation (0.49 in the solver: the linear element locks as the ratio nears 0.5 (nearly incompressible).)Rubber · Specific heat: government (NBS J. Res. 68A, Table 7; values observed for unvulcanized NR by Bekkedahl and Matheson), 25 °C
5
Thermal Conductivity of Soft Vulcanized Natural Rubber: Selected Values (AD 643325)Defense Technical Information Centerarchived copyRubber · Thermal conductivity: government selected value (US Army Natick Laboratories TR 66-49-PR, 1966), soft vulcanized natural rubber, 25 °C

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 POM/Acetal stronger than Rubber?

Plastic POM/Acetal is stronger: its yield strength is 69 MPa against tensile strength 23 MPa for Rubber (3x).

Which is lighter, Plastic POM/Acetal or Rubber?

Rubber is lighter: 960 kg/m³ against 1,420 kg/m³ for Plastic POM/Acetal.

Which is lighter for the same job, Plastic POM/Acetal or Rubber?

For the same stiffness or strength: Plastic POM/Acetal is lighter for a strong rod or tie, strong beam, strong panel or plate.

Part that must be	Plastic POM/Acetal	Rubber
Strong rod or tie	lighter	2.03x heavier
Strong beam	lighter	41% heavier
Strong panel or plate	lighter	17% 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 is more ductile, Plastic POM/Acetal or Rubber?

Rubber stretches further before it breaks: 830% elongation at break against 75% for Plastic POM/Acetal.

Thermal

Which conducts heat better, Plastic POM/Acetal or Rubber?

Plastic POM/Acetal conducts heat better: 0.4 W/m·K against 0.151 W/m·K for Rubber.