Before the term reached the zeitgeist, coffee giant Starbucks went “viral” using their disposable cups as mini-billboards, gaining visibility and growing their brand as consumers carried their drinks with them, years before social media or selfies. By their own estimate, the chain dispatches about 6 billion of these advertising vessels annually.

However, because the paper cups get manufactured with a liner made of plastic, they aren’t recyclable.

Of course, Starbucks doesn’t want to see the disposable cup go away entirely—unlike some coffee shops—and in 2018, the chain pledged $10 million towards the development of a more sustainable alternative to the current to-go hot cup through the NextGen Cup Challenge. A year ago, after evaluating nearly 500 designs from over 50 countries, the NextGen Consortium chose 12 winners, and, starting this week, Starbucks will test one iteration at locations in Vancouver, Seattle, San Francisco, New York, and London.

The experimental cups come lined with a material called Bio-PBS, or bio-based polybutylene succinate, made by Mitsubishi Chemical. The substance can withstand high temperatures, is compostable, and can be applied using existing extrusion coating machines, blown film extruders, and injection molding machines designed for traditional petro-based PBS.

Bio-PBS lined paper cups are part of Starbucks’ efforts to meet their sustainability goals, which includes a 50% reduction in waste sent to landfills by 2030.