Many sneakers can be heavy on non-biodegradable synthetics, which ultimately contributes to the pile-up of plastic that’s seeping into every surface on the planet (even the atmosphere ). But, luckily, there's a growing host of footwear brands working to come up with a more sustainable solution: styles with all the bounce, comfort, and swag that we look for in a tennis shoe , without all of the waste and environmental degradation that's commonly associated with sneakers.