Polyethylene is a fancy name for a type of plastic. You know what plastic is, right? It's that stuff that can be made into all sorts of things like water bottles, toys, and even cars!
Polyethylene is made up of lots and lots of tiny little pellets called polymers. Imagine a bunch of tiny beads stuck together. When they're heated up, they melt and can be molded into different shapes. It's kind of like when you play with play-doh and you can make it into different things.
There are two types of polyethylene: high-density and low-density. High-density polyethylene is really strong and can be used for things like pipes, trash bags, and even bulletproof vests! Low-density polyethylene is softer and more flexible, so it's good for things like plastic wrap and plastic bags.
Polyethylene is cool because it's really cheap to make and it's really easy to recycle. So next time you see a plastic water bottle or a plastic grocery bag, you can remember that it's made of polyethylene!