Plastic PMMA vs. Plastic POM/Acetal

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

Plastic PMMABulk polymer (molded or machined)

Plastic POM/AcetalBulk polymer (molded or machined)

Mechanical	Plastic PMMA	Plastic POM/Acetal
Yield strength	not given (tensile used)	69MPa1
Ultimate tensile strength	80MPa216% stronger	69MPa1
Compressive strength	110MPa2	124MPa113% stronger in compression
Flexural strength	115MPa2	99MPa1
Elongation at break	5.5%2	75%113.6x more ductile
Young's modulus (stiffness)	3.3GPa218% stiffer	2.8GPa1
Density	1,190kg/m³219% lighter	1,420kg/m³3
Strength to weight	67.2kN·m/kg38% higher	48.6kN·m/kg
Stiffness to weight	2.77MN·m/kg41% higher	1.97MN·m/kg
Poisson's ratio	0.372	0.351
Shear modulus	1.2GPa16% stiffer in shear	1.04GPa
Bulk modulus	4.23GPa36% higher	3.11GPa
Speed of sound	1,665m/s19% faster	1,404m/s

Stiffness against densityHigher and further left: stiffer for its weight

Strength against densityHigher and further left: stronger for its weight

Thermal	Plastic PMMA	Plastic POM/Acetal
Thermal conductivity	0.19W/m·K2	0.4W/m·K12.11x more heat through a fin
Thermal expansion	0-50 °C70µm/m·K21.74x less	mean122µm/m·K1
100 mm part over a 50 °C swing	350µm growth1.74x less	610µm growth
Specific heat	1,470J/kg·K2	average -18 to 100 °C1,465J/kg·K1
Heats up and cools (diffusivity)	0.109mm²/s	0.192mm²/s1.77x faster
Thermal shock resistance	41.5W/m	52.5W/m27% more resistant
Melting point	not sourced	175°C1
Max service temperature	80°C2	HDT 1.8 MPa125°C1

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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Sources3 documents: DuPont, Röhm

Plastic PMMA: Röhm PLEXIGLAS GS 0F00 cast acrylic sheet, typical values at 23 °C / 50 % RH (Röhm Technical Information Ref. No. 211-1)
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

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
PLEXIGLAS GS and XT Technical Information (Ref. No. 211-1)Röhmarchived copyPlastic PMMA · Ultimate tensile strength: typical, 23 °CPlastic PMMA · Compressive strength: compressive yield stress, typicalPlastic PMMA · Flexural strength: typicalPlastic PMMA · Elongation at break: typicalPlastic PMMA · Young's modulus (stiffness): typical, short-termPlastic PMMA · Density: typicalPlastic PMMA · Poisson's ratio: typicalPlastic PMMA · Thermal conductivity: typicalPlastic PMMA · Thermal expansion: 0-50 °CPlastic PMMA · Specific heat: typicalPlastic PMMA · Max service temperature: max. permanent service temperature
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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')

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 PMMA stronger than Plastic POM/Acetal?

Plastic PMMA is stronger: its tensile strength is 80 MPa against yield strength 69 MPa for Plastic POM/Acetal (16%).

Which is lighter, Plastic PMMA or Plastic POM/Acetal?

Plastic PMMA is lighter: 1,190 kg/m³ against 1,420 kg/m³ for Plastic POM/Acetal.

Which is stiffer, Plastic PMMA or Plastic POM/Acetal?

Plastic PMMA is stiffer: Young's modulus 3.3 GPa against 2.8 GPa for Plastic POM/Acetal, so the same part in Plastic PMMA deflects less under the same load.

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

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

Part that must be	Plastic PMMA	Plastic POM/Acetal
Stiff rod or tie (tension)	lighter	41% heavier
Stiff beam (bending)	lighter	30% heavier
Stiff panel or plate	lighter	26% heavier
Strong rod or tie	lighter	38% heavier
Strong beam	lighter	32% heavier
Strong panel or plate	lighter	28% 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 PMMA or Plastic POM/Acetal?

Plastic POM/Acetal stretches further before it breaks: 75% elongation at break against 5.5% for Plastic PMMA.

Thermal

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

Plastic POM/Acetal conducts heat better: 0.4 W/m·K against 0.19 W/m·K for Plastic PMMA.

Which expands less with temperature?

Plastic PMMA expands less: 70 µm/m·K against 122 µm/m·K for Plastic POM/Acetal.