Some plastic materials are better used where transparency is important, in this case polystyrene or polymethylmethacrylate. Which is used depends also on the other properties (ca it be moulded well, for example).
Most people expect that plastics are good insulators of electricity, but not all are. The loaded polythene will conduct electricity.
Flexibility is important and in this case the polypropylene is the most flexible. The properties of plastics can be altered to some extent to suit the product, but you could not make stacking chairs from polystyrene for example.
All plastics can be moulded. Some, like polystyrene (not used here), can take precise detail from the mould, but the ease with which many copies can be produced without using much energy is one of the key properties of plastics.