Ok I have both, I was just asked why. What would your responses be? Wet vs non wet conditions would be my first response. What else would you say to someone that asked why you have both a down and synthetic of similar warmth ...
I use down for backpacking and backcountry skiing. I don't plan on getting wet or being around pointy things or abrading against things. Its warmer, lighter, and packs smaller. But if you get a hole in it, bad news...
I used synthetic for ice climbing and sometimes rock climbing when I could get wet and will definitely be around pointy things and could be rubbing against rock or ice. A tear or hole is no big deal in synthetic.
I don't own a down jacket because it's only useful if I'm not moving. Every time I'm tempted to buy a fancy lightweight down jacket I remember that I'll sweat through the damn thing in 5 minutes next time I'm out ice climbing or hiking.
Down is great as long as you're not a fat, sweaty pig.
I don't own a down jacket because it's only useful if I'm not moving. Every time I'm tempted to buy a fancy lightweight down jacket I remember that I'll sweat through the damn thing in 5 minutes next time I'm out ice climbing or hiking. Down is great as long as you're not a fat, sweaty pig.
Wouldn't you sweat through a synthetic jacket too? I don't wear insulating layers when I'm doing anything aerobic.
For the midlayer, hands down synthetic. There are extremely few down garments that can compete in breathability with a solid synthetic garment. Moreover, as you start to sweat the down will collapse. Also... we tend to do a lot of climbing in the midlayer. Down stuff tends to be significantly more fragile so again it's not a good choice for a midlayer. Only time I'd recommend a down sweater over a high end synthetic midlayer (like the Arc'Teryx Atom) is for high altitude mountaineering where you need maximum warmth/weight ratio and it'll be dry all the time. Packability shouldn't be a consideration since you rarely take this layer off anyways.
For a parka/belay jacket/summit piece no brainer: down. You'll want something with 700 or better fill power (keep in mind this is only a piece of the puzzle) and bomber construction (if you just want warmth get something like the Marmot Greenland). Hands down (no pun intended) the best down jackets (for the price) I've tried have been the Rab Neutrino and the Millet Expert. The neutrino is slightly warmer and lighter but the Expert has a better fit and bomber construction (ceramic reinforcements). If money is no object then feathered friends, Valandre, and other handmade parka manufacturers put out nice stuff.