10:50 p.m. on March 2, 2012 (EST)
Maybe it is time for me to chime in, since I have used both down and synthetic bags with shells including cotton, plain old ripstop nylon, wpb such as various kinds of Goretex, and microfiber, such as Pertex, in "cold" conditions ranging from -40C and below (very dry, always - I stay away from polar oceans, so Antarctic inland, Denali high altitude, Tetons midwinter) to temperatures hovering around 0C/32F with mixed rain and snow, melting snow, etc. (Sierra, Cascades, Rockies).
Down - definitely the best choice, IF... conditions are dry and you can keep the bag dry. If you are highly experienced and diligent, you can stay dry in Sierra/Cascades transitional conditions (0C down to 15-20F). But when I go out with Scouts or less experienced people, then it is synthetic, including when I have to share a tent with the less experienced adult. New England, I always stuck with synthetics, having been out in the Presidentials when a Noreaster blew in, sucking in warm, very wet air with rain and melting the snow that was on the ground (unless I was pretty sure of the forecast that it would stay at least below the 15F mark).
Drying wet bags - Dewey is absolutely right - you can't dry down in the field. If you got it wet because of mixed snow/rain, or because your tent partner dragged wet snow in with him, you have a wet bag until you get home. Sierra Designs et al promise great things with their magic polymer down. Having no experience with it, plus its being brand new to the market, I am extremely skeptical (as I am of all "new, wonderful, greater" things that are life and limb critical - I learned a thing or two from having survived this many decades).
Synthetic - a lot has changed with synthetics since the first ones I used. If you get them wet, one thing you can do with the latest ones is roll them up very tightly several times and squeeze a lot of the water out (this does not work with down). This allows the fill to fluff up a bit. If you then put a VBL liner in, remove your wet clothes and put on dry longies (if you have them), you do get a bit of warmth. It ain't toasty warm if it is cold outside the bag, but it is a lot warmer than if you had no bag at all. Yeah, you are warming the water that remains (a lot less after squeezing). You may still be shivering, but I haven't had anybody get hypothermia doing this in an emergency (if you soaked the bag, it IS an emergency! we did put them in a tent on closed cell foam pads and kept them supplied with chemical hand warmers and hot food and drink - but remember that the human body contains something like 50-70 kg of water, so pouring 1 liter of "hot" drink at the maximum standable 43C/110F isn't going to add much to the body heat of a border hypothermic person).
The best synthetic currently in my experience is Primaloft. I have gotten my Dolomiti jacket pretty damp while belaying someone on an ice climb on a wet, "frozen" waterfall. Then squeezed it out and put it back on, and was fairly comfortable (thanks in part to exercising hard on the climb). I should have had my ID eVent belay jacket on, but had left it at the bottom of this "short" climb.
I am not saying this will be the same for everyone - witness the number of companions I have had on snowshoe tours and backcountry ski trips who got soaked while I stayed completely dry. Experience teaches you a lot about how to handle wet conditions (as everything else outdoors). These days, I rarely get the down in my jackets and sleeping bags damp, though I am always very aware of the possibility and continuously monitoring myself (and companions).
Back to the OP - Tom, I believe you have enough experience that it doesn't really matter whether you use down or Primaloft. I don't say this for everyone who reads Trailspace, though. You have a few trips under your belt on the rim of Yosemite Valley, which is a pretty damp "winter" environment.
Rick asked:
I could never for the life of me figure out why TNF not only supplied you with a compression sack but a mesh bag for long term storage. Do people actually use these things? I mean seriously. They still compress the bag to some extent.
To me for seasonal storage this kind of defeats the purpose doesn't it? I feel hanging is the way to go.
Rick,
Yeah, hanging the bag, or even stacking them up on a shelf is a good way to go for long term storage. But not many people have enough closet or shelf space to do this (at least not when you have as many bags as Barb and I have per person). Using a large mesh bag or a cotton or cheesecloth laundry bag compresses the bag only a minimal amount (assuming you use a large enough bag), and lets the sleeping bag (and down jackets and down pants) breathe. Obviously, make sure the bag is thoroughly dry and aired out (or freshly washed and completely dried and aired) before you put it in even a very breathable storage bag. This takes up less space than hanging in the closet or stacking on shelves (or, in our case for a few years, on the Kid's bunk beds when he headed off to college). And the cotton storage sacks keep the bag from collecting dust and slows the critters from making it their home. Then again, our bags don't stay stored very long between uses.