If your friend asked, "why are plastics good insulators," what would be the best reply? electron flow is necessary for electrical current. plastics are able to readily accept electrons, and this makes them good insulators. in order for electricity to flow, you must have atoms that are able to easily lose or accept an electron. plastic atoms have this characteristic, which makes them a good insulator. materials like plastics do not have any loosely bound electrons in their outer shell making it difficult, if not impossible, for electrons to move between atoms. the most important quality of an insulator is that its atoms are balanced with the same number of protons and electrons. plastic atoms have this characteristic which makes them an excellent insulator.