Plastic PLA vs. Plastic Polypropylene

Compare Plastic PLA vs. Plastic Polypropylene strength, stiffness, weight and thermal properties.

Plastic PolypropyleneBulk polymer (molded or machined)

Mechanical	Plastic PLA	Plastic Polypropylene
Yield strength	52.5MPa11.59x stronger	33MPa2
Ultimate tensile strength	52.5MPa1	not stated (yield given)
Flexural strength	96.8MPa1	not sourced
Elongation at break	7.8%1	not sourced
Young's modulus (stiffness)	3.25GPa12.24x stiffer	1.45GPa2
Density	1,240kg/m³1	900kg/m³238% lighter
Strength to weight	42.3kN·m/kg15% higher	36.7kN·m/kg
Stiffness to weight	2.62MN·m/kg1.63x higher	1.61MN·m/kg
Poisson's ratio	not sourced	base material0.423
Shear modulus	not sourced	0.511GPa
Bulk modulus	not sourced	3.02GPa
Speed of sound	1,619m/s28% faster	1,269m/s

Stiffness against densityHigher and further left: stiffer for its weight

Strength against densityHigher and further left: stronger for its weight

Thermal	Plastic PLA	Plastic Polypropylene
Thermal conductivity	base material0.13W/m·K4	base material0.17–0.22W/m·K3
Thermal expansion	not sourced	base material80–100µm/m·K3
100 mm part over a 50 °C swing	not sourced	450µm growth
Specific heat	base material1,200J/kg·K4	not sourced
Heats up and cools (diffusivity)	0.0874mm²/s	not sourced
Thermal shock resistance	not sourced	28.6W/m
Melting point	152°C1	not sourced
Glass transition	59.1°C1	not sourced
Max service temperature	HDT 0.455 MPa58.8°C1	HDT 0.45 MPa90°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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Sources4 documents: UltiMaker, LyondellBasell, INEOS Olefins & Polymers USA, NatureWorks

Plastic PLA: Ultimaker PLA, 3D-printed specimens, XY (flat) orientation; Ultimaker S5 Pro, engineering intent profile, 0.15 mm layer height, AA 0.4 print core, 100% infill, Cura 4.9, printed one-at-a-time, conditioned >=24 h at room temperature. TDS dated April 20, 2022.
Plastic Polypropylene: LyondellBasell Moplen HP501H polypropylene homopolymer (general purpose), typical ISO values

1
Ultimaker PLA Technical Data Sheet, v5.00UltiMakerarchived copyPlastic PLA · Yield strength: typicalPlastic PLA · Ultimate tensile strength: typical, peak stress (= stress at yield)Plastic PLA · Flexural strength: typicalPlastic PLA · Elongation at break: typicalPlastic PLA · Young's modulus (stiffness): typicalPlastic PLA · Density: typicalPlastic PLA · Melting point: typicalPlastic PLA · Glass transition: typicalPlastic PLA · Max service temperature: HDT 0.455 MPa (printed specimens)
2
Moplen HP501H Product DataLyondellBasellPlastic Polypropylene · Yield strength: typical, tensile stress at yield ISO 527Plastic Polypropylene · Young's modulus (stiffness): typical, tensile modulus ISO 527Plastic Polypropylene · Density: typical, 23 °C ISO 1183-1Plastic Polypropylene · Max service temperature: HDT 0.45 MPa (ISO 75B), unannealed
3
Typical Engineering Properties of PolypropyleneINEOS Olefins & Polymers USAarchived copyPlastic Polypropylene · Poisson's ratio: base material: polypropylene homopolymer family (INEOS Olefins & Polymers USA, Typical Engineering Properties of Polypropylene)Plastic Polypropylene · Thermal conductivity: base material: polypropylene homopolymer family (INEOS Olefins & Polymers USA, Typical Engineering Properties of Polypropylene)Plastic Polypropylene · Thermal expansion: base material: polypropylene homopolymer family (INEOS Olefins & Polymers USA, Typical Engineering Properties of Polypropylene)
4
Engineering Properties of Ingeo BiopolymerNatureWorksarchived copyPlastic PLA · Thermal conductivity: base material: NatureWorks Ingeo biopolymer, amorphous sheet, 25 °CPlastic PLA · Specific heat: base material: NatureWorks Ingeo biopolymer, amorphous sheet, 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.

Plastic PLA is 3D printed: its properties depend on build direction and print settings; these are typical values.

Questions

Mechanical

Is Plastic PLA stronger than Plastic Polypropylene?

Plastic PLA is stronger: its yield strength is 52.5 MPa against 33 MPa for Plastic Polypropylene (1.59x).

Which is lighter, Plastic PLA or Plastic Polypropylene?

Plastic Polypropylene is lighter: 900 kg/m³ against 1,240 kg/m³ for Plastic PLA.

Which is stiffer, Plastic PLA or Plastic Polypropylene?

Plastic PLA is stiffer: Young's modulus 3.25 GPa against 1.45 GPa for Plastic Polypropylene, so the same part in Plastic PLA deflects less under the same load.

Which is lighter for the same job, Plastic PLA or Plastic Polypropylene?

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

Part that must be	Plastic PLA	Plastic Polypropylene
Stiff rod or tie (tension)	lighter	1.63x heavier
Stiff beam (bending)	lighter	9% heavier
Stiff panel or plate	5% heavier	lighter
Strong rod or tie	lighter	15% heavier
Strong beam	1% heavier	lighter
Strong panel or plate	9% heavier	lighter

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).

Thermal

Which conducts heat better, Plastic PLA or Plastic Polypropylene?

Plastic Polypropylene conducts heat better: 0.195 W/m·K against 0.13 W/m·K for Plastic PLA.