What do the numbers 1 to 7 at the bottom of a plastic bottle mean

What do the numbers 1 to 7 at the bottom of a plastic bottle mean

If you want to know which number represents the type of material used in plastic bottles, you should know that we should correctly use the number 1 in the triangle at the bottom of plastic bottles: pet polyethylene terephthalate, common mineral water bottles, carbonated beverage bottles, etc