Down vs. Synthetic depends on preference and anticipated conditions. Unfortunately, it is the unanticipated conditions that can casue the problems. Neil is right in that there is not much that is going to happen on a bike tour (unless you are in Mongolia)affecting your sleeping bag that is life threatening. Mountaineering is my other passion and I have 3 synthetic (-20,+25,+40) bags and 1 down bag (sub zero). The down bag seldom gets used for all the reason listed. The new synthetics are almost as warm and as compressible as down. The +25, Marmot Pounder Plus, is light and is used on ski trips as well as bike tours. The + 40 is a summer bike tour /backpacking bag. I think most folks can get away with either down or synthetic fill material. Economics, anticipated present and futures uses, weight, size, and personal prefence are all factors.

The sleeping bag (Marmot Pounder Plus,+25 degrees and <2 pounds) is in the yellow compression sack, the tent in the blue. The orange is a full length Thermarest Prolite 4 (good for summer and snow)


The water bottle gives the bags some scale. The sleeping bag and our tent compress down into packages the size of a small loaf of bread


Unexpected, but not unanticipated in August- a few hours earlier we were climbing in shorts. Generally not encountered on bike trips