These are three of the most popular All-Clad stainless steel cookware collections. They differ in the number of bonded layers of metal and the types of metal used in their construction. D3 is three-ply cookware that’s made from two layers of stainless steel surrounding a layer of aluminum. This is the least expensive of the three collections and the most popular.D5 is five-ply cookware with five alternating layers of steel and aluminum. This cookware is more durable than D3, but it’s also more expensive. Copper Core also uses five layers of metal, but the center layer is made of copper. While pricey, this five-ply All-Clad cookware is prized by professional chefs and serious home cooks.