Here's why:

* Durability: PP is strong and relatively rigid, making it suitable for holding liquids.

* Lightweight: PP is lightweight, which is important for portability.

* Heat Resistance: PP can withstand temperatures up to around 130°C (265°F), making it suitable for hot drinks.

* Cost-effectiveness: PP is a relatively inexpensive material to produce.

However, other types of plastic can also be used for cups, depending on the specific application:

* Polyethylene (PE): This is another common choice, particularly for disposable cups.

* Polystyrene (PS): Used for disposable cups, but less common now due to environmental concerns.

* Polycarbonate (PC): Used for reusable cups due to its high durability and transparency.

When you see a recycling symbol on a plastic cup, the number inside usually indicates the type of plastic:

* #5 is the recycling code for polypropylene (PP).

It's worth noting that not all cups are made from the same type of plastic. The specific type of plastic used will depend on the intended use of the cup.