Olefin is resistant to moisture, mold, and mildew and makes a good carpet for basements and outdoors. It’s tougher than nylon, but not as comfortable to walk on.
 

Acrylic is often used as an inexpensive alternative to wool. It’s not widely available.
 

Wool is the premier carpeting and the only natural fiber made into carpets. It’s durable and stain-resistant, and it’s considered an eco-friendly floor covering.