>the friend had said polymers, not plastic. What is the difference, please?

a question! a palpable question!!
without going into a lot of scientific flummadiddle, which no one wants to see, suffice it to say that plastics are a subset of polymers, which are formed by a chemical reaction in which two or more molecules combine to form larger molecules that contain repeating structures. polymers do occur naturally, but not plastics -- which are artificial. ain't the circularity grand?