ability of a material to transmit electricity or heat
electrical conductivity: measured in siemens per meter (S/m)
thermal conductivity: measured in watts per meter-kelvin (W/m-K)
metals exhibit high conductivity due to free electron clouds: copper, silver, gold
insulators resist flow: glass, rubber, ceramics
semiconductors have tunable conductivity via doping, foundation of transistor technology
electrolytic conductivity depends on ion concentration, used to measure water purity
superconductors achieve zero electrical resistance below critical temperature
inverse of electrical conductivity is resistivity