The M218N is a Natural-colored PP plastic flat lip balm lid. Polypropylene (PP) is marked with the resin identification code of 5. PP is less flexible than LDPE, somewhat stiffer than other plastics, reasonably economical, and can be translucent, opaque, or of any color. PP has very good resistance to fatigue, and has an extremely high melting point (320 degrees Fahrenheit or 160 degrees Celsius). Natural-colored plastic is not actually colored. This is the natural color of the plastic, which is a milky translucent color. This translucent color shows product level, or how full (or, if you're a pessimist, how empty) the container is.