Why is It Desired That an Electrical Insulating Material Have Less Thermal Conductivity?

Since critical radius of insulation decides whether heat transfer would increase or decrease upon further increasing the thickness.

These both techniques are employed if you want to regulate the heat transfer .in case of electrical wires we don’t want our wires to melt down so we employ thickness less than critical radius so that there is continuous heat loss.

And under some circumstances if you want to reduce the heat transfer like pipe carry the steams then we increases thickness beyond critical radius.