The Covid-19 pandemic has caused havoc for manufacturers shipping goods around the world. Just ask executives at Apple why they shipped empty cardboard boxes from the U.S. to Asia, the reverse of the usual route.

Last February, Apple’s Singapore distribution center ran out of the brown mailing boxes needed to fulfill a spike in iPad orders from China, stemming from increased demand for remote-learning devices, said a person with direct knowledge of Apple’s logistics operations. While the specially designed iPad mailing boxes were originally made in China, the only solution that avoided delays for customers was to fly in a shipment of the boxes that was sitting unused at a warehouse in the U.S.