If your friend asked, "why are plastics good insulators? " you would reply: 1. 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. 2.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. 3. plastics and rubber atoms have the same number of neutrons and electrons. this allows them to share electrons with other materials, allowing electric current to flow freely. 4. 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.