Yesterday marked the first day of summer, so the thought of wearing fleece is far from most folks’ heads. But come fall, you will see the synthetic insulation material everywhere, from hardcore outdoor enthusiasts to “basic” people with an affinity for pumpkin spice lattes. In fact, you’d be hard-pressed to find someone that doesn’t own any fleece product, whether it’s a hat, jacket, or gloves.

But while fleece is generally seeen as a material favored by people that value getting outside, a new study found that fleece may actually hurt the environment in a major way. Following up on earlier research on the presence of fibrous microplastics in marine environments, Patagonia, who sells a lot of fleece, commissioned a study with the Bren School of Environmental Science and Management at the University of California, Santa Barbara to examine the impact of fleece products on our waterways. While all the data has not yet been released, some of the results found that when a single fleece jacket is washed in the laundry, it can shed up to 250,000 fibers. Those fibers are too small to be filtered out by washing machines or the wastewater treatment facilities they make their way to, so they end up in watershed areas where small aquatic species injest them. Those species, and the ones that consume them, can have their health negatively impacted by the microfibers. Some of those fibers even end up in the fish that are consumed by humans.

Based on an estimate of 100,000 Patagonia fleece jackets being watched annually, the resulting fibers released into waterways would equal that of 11,900 plastic grocery bags. The study also found that jackets that are older can release up to 80 percent more fibers than a new jacket.

To its credit, Patagonia is not trying to downplay its role in this process. While also noting the role that better washing machines can play, the company acknowledged that it and other apparel companies contribute to the microfiber pollution and outlined steps it would be taking to address the issue. In addition to conducting further research, Patagonia plans to look at the role the design of its products plays in microfiber shedding and also to explore the development of new materials that shed less.

Justin Tejada is a writer and editor based in New York City. Follow him on Twitter at @just_tejada.