The thermal resistance is the ratio of length of the rod of the material  and the product of the coefficient of  thermal conductivity and the area of cross-section of the rod.

                          R = l/KA

Where, l= length of rod

             K = thermal conductivity

             A = area of cross-section.

If the resistance increases thermal conductivity decreases and vice versa.

The SI unit of thermal resistance is second°C/kilo-calorie.