When outdoor enthusiasts, beckoned by winter’s spectacular mountain peaks, quiet forests, and icy adventures, pull on their merino wool base layers and slip into wool socks, many do so believing they’re wearing quality gear that’s good for the environment too. 

That’s no accident—the wool industry has long used fossil fuels’ (well-earned) bad rap to its advantage, touting its “natural” and “biodegradable” fibers as the perfect foil to materials like polyester and nylon. In a recent “Wear Wool, Not Fossil Fuel” ad campaign from the Woolmark Company, three people emerge from a pool of dark, viscous oil. They peel away the layer of sludge, revealing “clean” wool-based garments and smiling faces, then stroll toward a pristine-looking forest. 

The reality is, by the time they reach our closets, most wool products are far from biodegradable. They’ve been dyed. They’ve been coated in chemicals to render them machine-washable and blended with synthetic fibers—usually the same fossil-fuel-based fibers the wool industry castigates.

Wool secured its place in the outdoor industry because it wicks moisture away from skin, providing insulation even in the most challenging weather. It’s also breathable and regulates body temperature, making it useful almost year-round. The wool industry has responded to outdoor enthusiasts' mounting concern about the climate crisis with greenwashed claims that the fiber is being produced in “regenerative,” “carbon neutral,” or even “climate beneficial” ways. 

But these claims quickly unravel. Wool isn’t a magical fiber nature simply provides to us—it’s a product of modern industrial, chemical, ecological, and genetic intervention, and as such, it’s contributing to devastating biodiversity loss. 

Shear Destruction, a Center for Biological Diversity and Collective Fashion Justice report I coauthored, charts the long, damaging path between farmed sheep and your outdoor winter attire. From habitat degradation caused by grazing sheep to the chemicals used to process the fibers, wool production is riddled with threats to wildlife. 

It often starts with sheep grazing on wildlife habitat that’s been deforested to make way for animal agriculture. While the environmental impacts of the meat industry have gained significant attention, the role of farmed animals used for fashion is often omitted from the conversation. And sheep, like cattle, are ruminants, which means they emit significant amounts of methane, a potent greenhouse gas. According to calculations by Collective Fashion Justice, the emissions associated with producing just one kilogram of greasy wool can match those stemming from 100-plus miles of gas-powered automotive travel.

Grazing sheep also tend to degrade habitat, and they're often deadly to native animals—they trample burrows and vegetation and compete for the forage native grazers need to survive. Fencing sheep in can fragment habitat, spread invasive weeds, and provide perches for raptors to prey on smaller species.

Domestic sheep also expose imperiled bighorn sheep in the mountains of the American West to deadly disease, like pneumonia. Rather than remove the source of the disease—the livestock—it’s common for state and federal wildlife officials to kill bighorn sheep that appear ill to prevent further spread. Wolves and coyotes, too, are frequently killed if they threaten wool-producer profits. 

The harms continue beyond the pasture. Between 35 percent and 60 percent of shorn wool is contaminated by grease, sheep sweat, dirt, vegetation, and feces. The process of cleaning this “greasy wool” involves scouring it with hot water and cleansing agents, producing effluent pollution that most often ends up being dumped into the environment as wastewater.

Despite wool’s clean, crunchy PR image, there’s simply no evidence that sheep can successfully sequester carbon in a variety of settings, nor that they can sequester enough to fully offset the emissions created by wool production. Even if every brand were to employ best practices, at the current scale of the wool industry, the increased land use that would be necessary would be devastating for wildlife. 

So what’s an eco-conscious outdoor lover to wear?

Since cotton can’t perform like wool, many worry that their only options lie in materials like polyester, acrylic, and nylon, all of which are derived from fossil fuels—meaning they contribute to the climate crisis long before they’re woven into clothing—and known for shedding microfibers, which pollute the ocean and harm wildlife. 

Thankfully, the world of fibers is broad beyond wool and polyester—and all of us can help create demand for better materials. Tencel, for example, is made from wood cellulose that doesn’t contribute to deforestation. Similar to wool, it’s been proven to absorb and release moisture and limit bacterial growth. Even brands that use wool have found that Tencel can outperform wool, cotton, and polyester. The soft, durable fibers wick three times faster and are 50 percent cooler than pure merino wool. And Tencel is washable, even without added synthetic coatings.

Tencel has excellent potential as a wool alternative, even for base layers and socks. There’s also incredible innovation underway to create fibers from banana plants to bamboo. However, the clothing industry has yet to make these alternatives as widely available as wool or polyester.

Keep in mind, the most sustainable gear is always what’s already in your closet. Resist the sales and shiny new gear you probably don’t really need. Enjoy your favorite wool sweater and socks for as long as you can, repairing holes or tears whenever possible. Remember that wool, like many other fabrics, doesn’t need to be washed every wear. By washing only when truly necessary, you’ll extend your gear’s lifespan and conserve water and energy.

Be wary of greenwashing, and pressure your favorite brands to commit to phasing out or reducing wool, while embracing alternatives that aren’t derived from fossil fuels. Companies are constantly developing new and better gear, and they could always be using that investment to develop innovative materials that will better protect people and our planet. 

Ultimately, the outdoor industry can’t afford to profit off our love of nature while promoting gear that’s harmful to it.