‘Down and synthetics both have pros and cons. Down is:
- Warmer for its weight,
- More compressible, and
- Less expensive,
- More humane (no live plucking), and
- Less adversely affected by moisture.
In specific regard to the issue of moisture sensitivity, I want to point out that synthetic insulations are absolutely not “warm when wet” like is often claimed. Moreover, down is so much more thermally efficient that even moisture-degraded down will be as warm for its weight as dry synthetic insulation. Finally, I’ve never had my down insulation get truly wet. Damp from high humidity, yes, but never wet from, say, having worn it in the rain or fording a river — that’s what my rain jacket and pack liner are for.
With the introduction of water-resistant down a few years ago, synthetics lost much of their wet-weather advantage. So now it’s mostly a cost and ethical consideration.
With few exceptions my preference is down. It’s the superior insulation, especially as one who tends to backpack in dry environments and as someone who can justify their purchases with extensive use. And, equally important, down is a better long-term investment — my heavily-used down pieces are almost as warm now as they were when new, whereas my synthetic-fill pieces are limp, lifeless, and needing replacement after just a season of daily use.’ http://andrewskurka.com/2015/backpacking-clothing-stop-insulated-jacket-pants/