- 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