China's investment in the petrochemicals industry is leading to excess capacity and falling profit margins for the industry as a whole, as a slower-than-expected rebound in demand means oversupply of materials that go into plastic-making such as ethylene and propylene is on the horizon. The construction of more than 20 petrochemical projects in China, set to be completed this year, will increase China's already significant market share of global manufacturing capacity to nearly a quarter by the end of 2020.