Pans that are good conductors heat up quickly, transfer heat quickly, and cool down quickly. Materials that conduct heat well include copper and aluminum. A pan made from a material that conducts poorly (such as cast iron) will heat up and transfer heat slowly, but will retain the heat for a long time. (See “The Materials”.)
Although it makes no difference what pan you choose when you boil water, it does make a difference when you boil milk. A good conductor can be used with any degree of heat, while a poor conductor should be used on low to medium heat, and only with care on higher heat. In a pan made from material that conducts heat well, milk will boil on high heat without burning or scorching, but not in a pan made from a lesser conductor. If you do use a poor conductor, pay closer attention to what you cook. Stir the contents of the pan more often, and adjust your heat carefully.