Interesting thread at The Lightweight Backpacker on various man-made fibers in sleeping bags. I ended up buying a synthetic-fill bag partly because it was super light, but also because synthetics insulate when wet, unlike down fill. One contributor begs to differ:

“Warm when wet” is sheer marketing hype that doesn’t exist in the real world of sleeping bag insulation. If your synthetic bag is saturated it is going to be some time before it is really comfortable — or even safe to be in. And if you have allowed your sleeping bag to get soaked — despite the availabliity of simple and effective options to do so — you are just as foolish as if a person with a down bag has allowed their bag to get soaked.

Some also note that synthetics lose their loft after a couple years. Mine’s still new so I’ll have to wait and see how that works out. But heck, if it gives me an excuse to wield my MasterCard at REI, how bad could that be?