Neither, apparently, does the author of this article in Yesterday's Slate.
Let's run down what we do know about the two options. The knock against fake fur is that nylon, acrylic, and polyester are made from nonrenewable petroleum._ And it takes some energy to process that oil into synthetic fibers: According to design consultant Kate Fletcher's Sustainable Fashion and Textiles, producing one kilogram of polyester requires 109 megajoules of energy, with 46 megajoules going toward the raw materials and 63 megajoules used to turn those materials into a finished fiber. Nylon consumes 150 megajoules per kilogram; acrylic, 157. A handful of designers are now making faux furs out of cotton, which uses just 50 megajoules per kilogram. (Producing cotton can take a lot of water, though.) The other major downside with fakes is that synthetic fibers take a really, really long time to break down -- anywhere from 500 to 1,000 years , if estimates for plastic-bag degradation are anything to go by.