Few people have heard of Huangyan, a booming industrial district of Taizhou, a city in eastern China’s Zhejiang province. Yet without it, many cars would likely be heavier, more expensive and less energy efficient, while everyday household goods would probably cost more. The town specialises in plastic components and moulding equipment – unassuming products that rarely make the news, but sit at the heart of modern manufacturing. For years, Huangyan’s producers have dominated this supply chain,...