If you mean the thermal barrier effect from the presence of a low-thermal-conductivity coating on a metal, then this effect manifests itself only when a heat flow passes through the metal. If there is no heat flow (your case), then even a meter or kilometer thick layer of paint will not change the temperature of the metal, which will be equal to the ambient temperature.

The thermal barrier effect of a low-thermal conductivity coating is manifested in cases when one side of the part is constantly heated, and the other is constantly cooled, which is the condition for the occurrence of a heat flux. The greater the difference between heating and cooling temperatures, the stronger the thermal barrier effect of the same coating.

Dear Sandeep Samane,

As is known, the materials have thermal expansion upon heating and shrinkage upon extrusion. This expansion and contraction is different for each metal, alloy or composite. The application of a coating leads to a change in heat transfer. Depending on the thermal conductivity of the coating can improve or worsen the desired positive result.

As an example, for metals with poor thermal conductivity, a coating with good thermal conductivity can be applied in order to improve heat dissipation during cooling. For metals with good thermal conductivity, a coating with poor thermal conductivity can be applied to reduce heat losses from heating the parent metal.

There are cases in which the coating on metal has only protective properties against corrosion without greatly deteriorating the thermal conductivity of the base metal.

Wishing you success in your research

It depends on the type and characteristics of the paint used. If you use thermal barier paints, rod core will be cool. If you use conventional oil based paints , rod core will remain hot. Metal infused oil paints may or may not effect the hear transfer.

Suggest the following paper:

https://www.sciencedirect.com/science/article/abs/pii/S0925838818307771