Until the advent of the covered hopper, bulk commodities like grain and cement were packed in sacks and loaded into boxcars. Loading and unloading was a tedious, time-consuming affair. In the 1930s, a few railroads took the basic coal hopper design and added a roof with loading hatches, enabling bulk commodities to be loaded from the top and unloaded from the bottom. In 1953, Pullman-Standard's 70-ton PS-2 became the first mass-produced covered hopper to be widely owned by U.S. railroads.