In most cases (not all) down is the correct answer. It is lighter and compacts smaller for a given comfort range. It also will last years longer. I have a 35 year old down bag that still keeps its loft. You don’t have to buy the 900 fill super down ($$$) for most bike touring situations. I tour with a 650 fill, 40 deg F down summer bag and along with layering clothing and a silk liner have slept comfortably on sub-freezing nights.
Down’s biggest drawback is it doesn’t insulate well if it is wet, and even being sufficiently damp will cause it to lose some of its insulation qualities. This has never been a problem for me on tour and I tour a lot in the rainy Pacific Northwest -- BC, Washington and Oregon. First thing in the morning before heading out and in the afternoon after the day’s ride is done I lay it out or hang it up to dry out (assuming it is not raining). Just a few minutes in a laundromat dryer on low will fluff it up nicely. I stuff my bag into a waterproof/breathable compression sack and the put it inside my Ortlieb waterproof/ breathable Packer Plus pannier for double protection during the day.
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On a trip you've got worry as a companion, for you're always concerned about what happens next and sticking to an itinerary. . . . on a journey you never have to worry. Something always happens next.
- Gordon Hempton: One Square inch of Silence
Last edited by Western Flyer; 03-01-13 at 03:12 PM.