Some materials, like wood, are insulators that block the flow of electricity. Conductors, such as copper, allow for electricity to flow through them. Other materials—semiconductors—can be either/or depending on conditions such as applied electric field or temperature. Unlike wood or copper or silicon, though, topological insulators (TIs) are an exotic state of matter that is conductive on the surface, but not in the bulk. Such unique material properties have great scientific implications and could be of use in a range of technologies, including wireless communications, radar and quantum information processing.