North Korea’s booming business in producing wigs for export to China once again drove bilateral trade last month, as rising wages push Chinese companies to seek cheap labor across the border.

The DPRK posted a four-year high in trade with China in November, with bilateral commerce reaching $224.3 million behind a jump in both exports and imports, according to official trade data released by China’s General Administration of Customs.

NK Pro analysis of line-item data shows that human and animal hair was North Korea’s top import at nearly $16 million last month, outstripping $13 million