Thermal Insulation is the reduction of heat transfer between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with especially engineered methods or process, as well as with the suitable object, shapes and materials. Heat flow is an inevitable consequence of contact between objects of differing thermal temperature. Thermal insulation in which thermal conduction is reduced or thermal radiation is reflected rather than absorbed by the lower-temperature body. The insulation capability of material is measured with thermal conductivity. Low thermal conductivity is equivalent to high insulating capability. In thermal engineering, other important properties of insulating materials are product density and specific heat capacity.
In fact, it is not just a reduction of heat transfer, this includes the resistance of heat transfer between objects of different temperature once they contact. For example, you happen to touch a naked wire without an insulator, since there is no resistance, there will be a transfer of the current to you. This is why there is what we call grounding. Thermal capability is high on water, this is why there should be an insulation in the condition that current is flowing within a wet surface or object. If you happen to have a contact with water and you suddenly get shocked by the flow of the current, there might be a wire that has a current leakage causing the current to flow towards you. This is why thermal insulation is absolutely needed. Electrical engineers are very sensitive to this topic because of the effect to human beings.