DWR stands for “durable water repellent.” It’s a coating that’s often applied to clothing to make it water-repellant. Imagine that very satisfying visual of water droplets simply beading up and rolling off the surface of your rain jacket. DWR works really well, but it’s traditionally made of chemicals known as perfluorinated chemicals (PFCs) that produce environmentally toxic byproducts, Patagonia explains. Many outdoor brands have developed—or are working on developing—new types of DWR that are not made with PFCs or with a different type of PFC that contains fewer carbon chains (six instead of eight), called C0 DWR. It’s difficult to create something that works as well as the PFC-based DWR but is environmentally friendly. Brands are upfront that there is a delicate balance between product performance and impact, which they’re trying to finesse.  Many brands use C0 DWR now, but other brands use proprietary PFC-free DWRs, meaning they do not share the actual chemical makeup they’re using. However, most do note their PFC-free DWR finishes are biodegradable and therefore won’t build up and harm the environment the way PFCs do.