You get a sense of Mac-vs-PC, Pepsi-vs-Coke, Israelis-vs-Palestinians in the great debate about whether the best sleeping bag should have down or synthetic fill.

This thread at Whiteblaze.net covers the controversy in pretty good detail.

If you listened to the Trailcast interview with the founder of Western Mountaineering, you heard the pro-down argument: down has the most warmth for the weight, holds its loft far longer and packs smaller. It has the small problem of becoming worthless as an insulator when it’s wet — a threat the Western Mountaineering guy calls overblown hype from people hawking synthetic bags (mind you all his bags use highly water-repellant fabrics, so it’s not like he’s taking any chances with his customers).

The pro-synthetics crowd insists that while down has its place on a dry, cold campout, poly-fill will keep you warmer in wet environments. A couple posts at the Whiteblaze thread noted that if you’re thru-hiking, you’re not really camping — you’re hiking with quick overnight breaks to sleep. In a camping situation you’ve got plenty of time to air out any kind of sleeping bag, but in a hiking situation where speed and distance are the premium, you might not want the hassle of keeping your down bag dry.

One thing a lot of folks don’t realize till they learn it the hard way is that moisture from your body is far more likely to get your bag wet over the course of a long campout. This will wet out a down bag after a few days, particularly in sub-freezing temperatures when you have no way to dry it out — the moisture will freeze inside the bag, then thaw when you try to sleep in it.

I’m in the middle of the road: I have a zero-degree down bag and a 25-degree PrimaLoft bag. Most of my campouts around the Bay Area will use the lighter synthetic bag but for snow-camping weekenders I’ll stick w/the down and just make damn sure to keep it dry.