Conductivities vary for material being greatest for metals, lower for nonmetals, even lower for liquids, and exceptionally low for gases. Diamond beats them all, and graphite beats diamond only if the heat can be forced to conduct in a direction parallel to the crystal layers. The material with the greatest thermal conductivity is a supercold form of liquid helium called helium II, which only exists at temperatures below 2.17 K. Since it is highly unlikely you will encounter this substance, it is really not worth thinking about except in the fact that it is an exceptional material. The preferred utensil for candy making is the wooden spoon.
Metals utensils conduct heat away and interfere with controlled crystallization.
One clo of insulation is equivalent to a lightweight business suit. The cook pot shown in the photograph to the right is quite unique. Pots of this sort are usually manufactured by stamping a single sheet of heavy gauge stainless steel or aluminum in a powerful metal press. Using copper in the base would increase the rate at which heat was transferred from the flames or heating element to the food, while using stainless steel on the sides would reduce the rate at which heat was lost from the food to the environment. Such an arrangement results in an effective cook pot that responds rapidly to changes in burner output.