One feature of aluminum racks is the products light-weight material. Athough Stainless steel is a heavier, stronger metal than aluminum.For example an aluminum 13-2 rack weighs 2.8 LBS empty and a stainless steel 13-2 rack weighs 4.3 LBS empty. As well as being lighter the aluminum is a better thermal conductor than stainless steel. Thus, when aluminum racks are used in vapor storage freezers, the aluminum conducts cold vapor from the bottom of the tank to the lids bottom surface. this keeps all of the products at a colder temperature throughout the tank.