US box shipments—that is, volumes of empty packaging materials sold to retailers, which in turn use them to ship orders to warehouses, storefronts and Americans’ doorsteps—fell to the lowest second-quarter reading since 2015, according to data from Fibre Box Association, a trade group. (Corrugated cardboard also goes into other items, such as 3D advertising displays, but since the vast majority is used for packaging, the industry tends to use “box shipments” and “corrugated cardboard shipments” interchangeably.)