HDPE vs PP vs PVC

High Density Polyethylene (HDPE), Polypropylene (PP) and Polyvinylchloride (PVC) that are manufactured and supplied in stock shapes (rod, sheet etc) are three common engineering plastics that fit into a similar category, both commercially and technically. All three are weldable, thermoformable, can be machined, and are in a similar price bracket that is at the lower end of the scale compared to other engineering plastics.

How do we decide which material to use and when?

Understanding the properties and characteristics of each material will help with material selection.

Mechanical Properties

PVC is stronger, stiffer and heavier than HDPE & PP. Higher stiffness allows for larger fabricated structures such as tanks and vessels, with the ability to either eliminate or reduce reinforcement rubbing.

	HDPE	PP - HC	PVC
Specific Gravity (Density)	0.96 (Floats in water)	0.91 (Floats in water)	1.44 (Sinks in water)
Tensile Strength	24 MPa	> 30 MPa	55 MPa
Stiffness (Tensile Modulus of Elasticity)	1000 MPa	1500 MPa	3000 MPa

HDPE

PP - HC

PVC

Specific Gravity

(Density)

0.96

(Floats in water)

0.91

(Floats in water)

1.44

(Sinks in water)

Tensile Strength

24 MPa

> 30 MPa

55 MPa

Stiffness (Tensile Modulus of Elasticity)

1000 MPa

1500 MPa

3000 MPa

Thermal Properties

PVC will expand (and contract) significantly less than HDPE and PP, but also has a lower maximum allowable service temperature.

Often plastics are used for their thermal insulation characteristics. All three materials are good thermal insulators, but PVC has the lowest thermal conductivity value (closely followed by PP) which means it is the best thermal insulator out of this range.

	HDPE	PP-H	PVC
Sustainable for Food Contact	Yes	Yes	No
Suitable for Drinking Water	Yes (Polystone PG100)	Yes (Non-UV grade only)	No
Ozone Resistance	Moderate	Good	Good

Other Characteristics

	HDPE	PP-H	PVC
Flammability Resistance (UL94)	Low Resistance HB	Low Resistance HB	Highly Resistance V0
Wear & Abrasion Resistance	Moderate	Low	Low
UV Resistance	Yes (Black & Yellow, not Natural)	Yes (UV Formulated Grade)	No
Colours (Stocked)	Natural (White), Black & Yellow	Beige	Grey