Nothing will ever be warmer/smaller than a down bag. I own fiber bags (heck, I have 6 total, 2 of them fiber) but they are not the warmest or most comfortable bags I have. You can choose a fiber bag, but know that it will die a little every time you stuff it up. You can spend a lot of money if you want, but it won't ever be the lightest thing available because manufacturers know that only novices buy synthetic bags so they add gimmicks that attract casual buyers (and add weight). Your only real hope for a truly lightweight bag is to buy an overbag/quilt from an ultralight shop (www.backpackinglight.com, et al) but bear in mind that those guys sell gossamer gear and expect to replace it every season.

I lived in Seattle for a year, and used nothing but down bags in the Cascades and the Olympics, so I scoff at the industry's push to get everyone into synthetics. Harvey Manning, Washington state resident and author of the bible: "Backpacking: One Step at a Time" (and 30 hiking guides) puts it best. When someone tells him that a wet down bag is useless he says: "Absolutely. So don't let your bag get wet."

If your sleeping bag gets wet you don't have a sleeping bag problem. You have a packing problem or a shelter problem.

Buy a Western Mountaineering bag, a lightweight drybag and a roll of compactor bags to line it. You won't be sorry.