During the Han Dynasty, what commodity did the Chinese trade for the first time?

I think it should be silk. The Hun Empire is Western Han's biggest enemy. At the beginning, Han took "Connections Through Marriages" policy to stablize the relationship with the Hun Empire. However, it didn't work well. According to the historical records, Hun Empire once required Han to give money, silk and other products so that they didn't invade Han.

Later, Emperor Wudi sent Zhang Qian to the Western Regions to persuade Daroushi (a country) to fight Hun Empire with Han. However, Daroushi refused. Then Zhang Qian returned. The route he took eventually became a trade route. Silk and other Chinese products were exported to the west.