Historically the three best choices are Down, Polarguard (especially 3D and Delta), and Primaloft, though Climashield sounds pretty good and will likely replace Polarguard as the most commonly use synthetic in the next few years. Each of these materials has different performance characteristics. You will need to decide the relative weighting of these characteristics to determine what insulation material will be the best for you. My preference is high fill power down in most situations. When >50F synthetic insulation can reach (if not beat) down for both weight and compression due to simpler constriction.
Down is “rated” in terms of “fill power”, that is the number of cubic inches one pound will fill. High fill power down has more down and less quills. There is a master’s thesis about a model of how down compresses. I would recommend staying away from any synthetics materials which are not Polarguard, Climashield or Primaloft since they will tend to be heavier for the same warmth and will will be less compressible. You might be interested in a message explaining why the Cocoon jacket switched from Primaloft to Polarguard Delta though there I tend to prefer primaloft because my experience matches Richard’s report on BPL (link broken) that primaloft retains more insulation that polarguard after use. The following table gives you a sense of what 30F bags would be like using different insulation:
|Factor||Polarguard||Primaloft PL1||500-600 Fill Down||>800 Fill Down|
|Purchase Cost||<$80 (low cost)|
$120-180 (high quality)
|Long Term Durability||4-7 years||3-6 years||10-15+ years||10-15+ years|
|~Comparative Stuff Size||2.2x||1.8x||1.4x||1x|
|Typical “30F” weight||2.7-3.5lb||3lb||2.2lb||1-1.5lb|
|Warm When Wet||Fair+ (dries faster)||Fair (absorbs less)||Poor||Poor|
The are many factors that should be considered besides warmth / weight including durability, drape, and what techniques need to be used to stability the insulation. There is an interesting thread on BPL about the interplay of warmth, weight, and loft and R values and loft, and EN 13537 and “clo” measurements.. The following is the best number I have found about the clo/oz numbers for a number of synthetics fills.
- Polarguard 3D, .63 clo/oz
- Polarguard Delta, .68 clo/oz.
- Climashield HL, .68 clo/oz.
- Primaloft Sport, .74 clo/oz.
- Climashield Combat, .79 clo/oz.
- Climashield XP .82 clo/oz.
- Primaloft One as .84 clo/oz
There is a fair amount of controversy about how important of “warm when wet” is for a sleeping bag. In truth… nothing is warm when wet. The advantage of the synthetics are they don’t absorb a lot of water so you can squeeze most of the water out of the air gaps and be back on the way to a dry sleeping experience. If down gets wet, it’s going to take time to dry (hints drying down), and you are going to be cold. The key is not to let you down bag get wet. There are new treatments which nano-coats down so that it doesn’t absorb water. This “waterproof” down isn’t waterproof, but it should behave a lot like a synthetic insulation which would be a huge improvement in wet conditions.
I recommend carrying sleeping bags / quilts in a drybag. Don’t take the bag out of the dry bag until you are somewhere where the bag won’t get wet. I used to think the getting down wet from splashing, rain, etc was an issue, but then I realized that in 30 years of camping, my sleeping bag or quilt hasn’t gotten wet enough to significantly impact the performance once. There have been several times when the shell has gotten damp, but I was able to dry it out enough in the field that it wasn’t a significant issue. I have had issues on extended trips in extreme cold… but this would effect all options. The solution is using a vapor barrier.
My dad had been using the same down sleeping bag for almost 25 years. It’s not quite as lofty as it was originally, but it’s still usable. I switched to using a down bag in 2000, and am very happy for the change.
There are some situations when I would consider a synthetic insulation: an extended trip in a location that has continuous, very damp conditions and the temperature was around freezing. If I was spending most of my time in locations in week+ long trips which were cool-cold and damp (say western Washington state) I would consider switching back to synthetic insulation.