Final answer:
Insulators are materials that don't allow electrons to flow freely, they have tightly bound electrons and therefore, do not conduct electricity.
Step-by-step explanation:
Materials that don't allow electrons to flow freely are called insulators.
Insulators are materials that have tightly bound electrons, which do not move easily from atom to atom and thus do not conduct electricity. They have a high electrical resistivity and prevent the flow of electric current.
Examples of insulators include rubber, plastic, glass, ceramic, and wood.
Learn more about Insulators and electrical conductivity