Seattle (CNN Business) After years of looking for greener alternatives to its paper cup — which is lined with plastic — Starbucks is testing out something new.

The company announced on Wednesday that it is testing out a compostable cup in five locations — New York, San Francisco, Seattle, Vancouver and London. Starbucks showed one of the cups being tested during its annual shareholder meeting on Wednesday.

The new cup looks just like Starbucks' current paper cup. The difference is inside, where instead of a plastic liner, a biodegradable liner serves as a barrier to make sure liquid doesn't leak out. That liner, developed by a Thailand-based company, makes the cup compostable in commercial composting facilities, which are rare.

Though the innovation may appear small to consumers, it's a big moment for Starbucks, which has been struggling to find a greener alternative to its cup for three decades.

Most recently, in 2018, Starbucks committed to the NextGen Cup Challenge. Along with other food companies, Starbucks and Closed Loop Partners, a recycling-focused investor group, crowdsourced solutions for greener cups from the public. In February, the company announced 12 winners, including greener cup liners, barriers and cups themselves.

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