Thermal conductivity, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction.
Heat transfer across materials of high thermal conductivity occurs at a faster rate than across materials of low thermal conductivity. Correspondingly materials of high thermal conductivity are widely used in heat sink applications and materials of low thermal conductivity are used as thermal insulation.  Thermal conductivity of materials is temperature dependent. In general, materials become more conductive to heat as the average temperature increases.  The reciprocal of thermal conductivity is thermal resistivity.