Typically, each plastic container has a number at the bottom (it is a triangular triangle with a number in the triangle).

If the number is "05" or more, it can be recycled; if less than "05", that is, "04" or less, or even no number, do not use or use the heating, because it will release toxic chemicals, 

The"7" number generally appear in the kettle, cups, bottles and other plastic products category.