Polythene is a light, strong plastic. People use it for shopping bags, thin sheets over food, and little bottles and boxes. It keeps water out, it bends, and it does not weigh much. This is the British name. In American English the same stuff is usually called polyethylene, or just plastic. You will hear polythene a lot in UK shops and on UK packaging: a polythene bag, polythene sheeting. Though actually, not every “plastic bag” is polythene, and food wrap is sometimes a different plastic. Chemists know it as a kind of polyethylene (PE). In daily life, nobody is thinking about the chemistry; they mean that familiar see-through or cloudy film. It is an ordinary, slightly technical household word in Britain, not a fancy one.

聚乙烯（PE）。英式說法；美式多說 polyethylene。日常多說塑膠袋、塑膠布那種塑膠，別和保麗龍混在一起。