Copper is perfect accumulator of heat
As we can see copper conducts the heat uniformly through
out the vessel, where as the steel vessel doesn't conduct uniformly.
Heat conduction is the flow of internal energy from a region of higher temperature to one of lower temperature by the interaction of the adjacent particles (atoms, molecules, ions, electrons, etc.) in the intervening space.
In general terms it is the transfer of heat from one molecule to another through a substance. Not all substances conduct heat at the same speed. Metals and stone are considered good conductors since they can transfer heat in a relatively fast manner when compared to other materials, but wood, paper, air, and cloth are poor heat conductors. A perfect vacuum is said to have a Zero conduction coefficient.
In general, solids are better conductors than liquids and liquids are better conductors than gases. Metals are much better conductors than non–metals. This is because metals have the “loosest” outer electrons, which are free to carry energy by collisions throughout the metal. They are excellent conductors of heat and electricity for this reason. Silver is the best, copper is next, and, among the common metals, aluminum and then iron are next in order. Wool, wood, straw, paper, cork, and Styrofoam, on the other hand, are poor conductors of heat. The outer electrons in the atoms of these materials are firmly attached. Poor conductors are called insulators.
So, for conduction of heat to occur, a material medium is always necessary. Conduction occurs mostly in solids. This can be understood if we see how solids, liquids and gases are bound to their respective atoms or molecules. Solids are tightly bound. The atoms or molecules cannot migrate from one site of the solid to the other, although the electrons can do so. Therefore Conduction is more predominant in solids.