These days, coffee waste is turned into everything from biofuel to recycled mugs. But a Finnish company is creating something new, coffee-based sneakers.

Rens used a Kickstarter fund to make their waterproof sneakers using old coffee grounds. “We actually took it and mixed it with recycled plastic granules made from used water bottles,” said Jesse Tran, co-founder and CEO of the company.

It takes a little more than a cup of used coffee beans to make a pair of shoes. This translates to 21 cups of joe. “The top part is mostly coffee waste,” says Tran.

Globally, we produce more than 23 million tonnes of coffee waste every year, according to Belgian sustainability researcher Gunter Pauli. And when it breaks down, it produces methane, according to greenhouse gas experts, about 30 times more harmful than CO2.

“In fact, we realized that only five percent of the world’s coffee waste is actually recycled,” says Tran.

Son Chu, co-founder and CTO of Rens, says, “We want to be a brand where we make products that are sustainable, but they’re cool, they have really cool features, people can actually use them.”

The Finnish shoe company has announced plans to use coffee grounds to create more wearable waste, including sportswear.