Which substances do not allow current to pass and why?

Substances that do not allow electric current to pass through them are called insulators or poor conductors. Examples include rubber, plastic, glass, dry wood, and air.

These materials do not conduct electricity because they do not have free-moving electrons. Their electrons are tightly bound within atoms, which prevents the movement of charge required for current flow.

As a result, insulators are widely used in electrical systems to prevent leakage of current and ensure safety, such as in wire coatings and protective coverings.