The best metals for conducting (transmitting) energy are, in this order, silver, copper, and aluminum. That is why electrical contacts are silver and copper, and also why wire is copper or aluminum. No one can afford silver electrical wire, I guess, although there are many small electrical components in computers that use silver to make the contact. As with wire, silver was not an affordable option for cookware, and I suppose it may even conduct a little too well for cooking. Meanwhile, copper was and still is the excellent affordable choice for rapid disbursement of energy, whether it be electricity or heat. Aluminum is the next choice, so for direct contact on a smooth top stove, the aluminum disc on the bottom of the stainless steel pan was the logical option. This line continued to be produced in the USA from 1986 until the late 90’s, when all production was moved out of the country. I believe it still continued with “China” production, but I am not sure if it still is manufactured there. I have lost both the trail and the interest for Revere Ware overseas production, and just concentrate on what was made in the USA.