Why combining aluminum and stainless steel is better for cookware:
Aluminum conducts heat incredibly well but lacks adequate heat retention
Stainless Steel retains heat for an incredibly long time but does a poor job of distributing it evenly
By layering the aluminum between the stainless you achieve a pan that holds heat and distributes it from the cook surface to the top of the rim.
Two type of stainless Kovea takes this a step further with this kit, by utilizing 18/10 stainless for the inner layer, and 430 Series for the outer layer you get improved stick resistance and durability on the inside, and a corrosive resistant exterior.