Serious athletes wear all those fancy fabrics for a reason: They help sweat evaporate before it sets on your skin, they keep you cool and the shoes are cushioned according to your sport.

But there are eco-alternatives too—sneakers made with recycled rubber soles (just be sure to recycle them when you're done), tops and pants that combine soy and organic cotton blends and coconut shells transformed into breathable fabrics. Look for companies with sustainable business practices like Patagonia, REI and Nau.