Below is a great resource from plasticpackagingfacts.org:
Plastic is often a more efficient material to choose than alternatives. That’s because plastics are incredibly energy efficient to manufacture and because they are lighter than alternative materials. Just two pounds of plastic can deliver 10 gallons—of a beverage. You’d need three pounds of aluminum, eight pounds of steel, or over 40 pounds of glass to bring home the same amount. Here’s a look at some plastic resins and some of the ways they’re commonly used in packaging applications
High Density Polyethylene (HDPE)
HDPE is the most widely used type of plastic. It’s used to make many types of bottles and containers. Unpigmented bottles are translucent, have good barrier properties and stiffness, and are well suited to packaging products with a short shelf life such as milk. Because HDPE has good chemical resistance, it is used for packaging many household and industrial chemicals such as detergents and bleach. Pigmented HDPE bottles have better stress crack resistance than unpigmented HDPE.
Low Density Polyethylene (LDPE)
Includes Linear Low Density Polyethylene (LLDPE)