When two objects of different temperatures are put in contact with one another, the faster moving particles collide with the slower moving particles, and energy is exchanged. The faster moving particles give up some energy and therefore slow down and the slower moving particles gain some energy and therefore speed up. This process, known as heat conduction, continues until an equilibrium is reached, where all the particles of both objects are moving at roughly the same speed. Therefore, the warmer object cools and the cooler object warms. The thermal current is directly proportional to the coefficient of thermal conductivity.
Different materials have different coefficients of thermal conductivity.
When heat is applied to a portion of a material, that heat will move through the material. This movement of heat through a material is called the thermal current. Depending on the composition of the atoms of that material, the heat may move very slowly, or it may move very quickly. This dependance is quantified by the coefficient of thermal conductivity. Each material has a unique coefficient of thermal conductivity.