Insularity and conductivity are terms related to electricity. Electricity is an energy current that is created when an electron is repelled out of its orbit by another electron that has been pushed out of orbit, in a domino effect. Atoms have negatively charges particles -- electrons -- that balance positively charged particles -- protons. When an electron is thrown out of orbit, a positive charge is created. If the electron is not thrown out of orbit easily, no charge is passed along. Silver, as one example, has very loosely bound outer electrons. Glass has very tightly bound outer electrons.
The "flow" of electricity is easier -- more conductive -- when the substance's outermost electrons are "free electrons," or electrons that are not tightly bound to the nucleus. Once one electron is thrown out of orbit, its negative charge repels the negative charges of other outermost electrons, passing the subsequent charge along through the substance like a flow. Substances with electrons that are more tightly bound create resistance to this flow. High resistance materials are called insulators. This is not always black and white. Electrons are bound along a continuum of strength, meaning that there are many grades of conductivity and insularity. Concrete and dirty water are poor conductors. Clean water is a poor insulator.
A list of well-known substances is helpful if you begin with the best conductors, work toward the poorer conductors, then go through the poor insulators to the best insulators. Silver is the very best electricity conductor, but it is expensive, so the second best is used more often: copper. After copper, there is -- in order of decreasing conductivity -- steel, aluminum, bronze, graphite, dirty water and concrete. A list beginning with the poor insulators, and progressing toward the best insulators might include, in order, pure water, plastic, dry wood, asphalt, rubber and glass.
Size matters, especially with conductors. A small copper wire can only conduct a given amount of electricity from a power source without burning in two. The dimension of the conductor determines its electrical carrying capacity. A thicker wire will conduct more electricity than a thinner one; and a copper plate will diffuse a charge in all directions. The reason wire is used in electrical circuits is that the shape of the wire directs the flow into a current. The reason thicker wire is used for higher voltages is to prevent the wire melting and creating a fire hazard.