And due to this translucent or opaque nature, it is used where transparency of the packaging is not required and the packaging require good impact strength and chemical resistance and very good resistance towards water and oxygen permeability.
HDPE is used for beverages, food and chemicals bottles and containers, also used in coating of chemical resistant piping.
Polypropylene is used in a wide variety of applications, including food packaging, textiles, laboratory equipment, automotive components, etc. It is unusually resistant to many chemical solvents, bases and acids. It is much less brittle than HDPE. PP has very good resistance to fatigue but less impact resistant than HDPE.
PP can be amorphous and crystalline and depending on that it will have different properties and uses. Density of amorphous PP is 0.855 g/cm3 and crystalline PP is 0.946 g/cm3.
Due to amorphous nature and low density of PP than HDPE, which is more crystalline, PP is transparent and used in cups and containers for food packaging. Crystalline PP is also used as food containers for high strength and chemical resistance but has low impact resistance than HDPE.
And due to good fatigue resistance plastic caps such as those on flip-top bottles, are made from PP.