The X73 was one of the most common sights in Conrail general merchandise trains. They hauled products such as fruits, vegetables, canned or bottled foods and drinks, paint, floor wax, liquid detergents, and many other water-based or chemical products needing protection from temperature extremes. Since they hauled such a variety of products, X73's could be found nearly everywhere. During late 1974, Fruit Growers Express built a total of 319 RBL insulated boxcars for the Penn Central and 75 cars for the Erie Lackawanna, all of which eventually became Conrail X73's in 1976. They had cushioned underframes, low ladders, and an overhanging, diagonal panel roof with no roofwalks.
Some cars also have additional, small reinforcement plates along the roofline.
These plates extend down to about the second rivet from the top and are located within the rivet lines. But not all Conrail X73's are not alike. Those originally owned by the Penn Central contained Dual Air Paks, though some also had pallets for assigned service. Cars originally owned by the Erie Lackawanna contained two air-activated Duo Pak Load Dividers plus pallets. Most people assume that Conrail owned these cars outright, like they did with their other boxcars.