A down bag in a lined compression sack won't take water either and compresses considerably  smaller.

MMMMM-like I wrote b4....to each there own. I run both synthetic and down. It is true the down is superduper light, compressible, and has great longevity if treated right. The thing of it is, due my personal experiences, I prefer synthetic on the water trips. Yes, they are a bit bulkier and heavier, and you do have to replace them more often because they wear out...It is worth it to me because a down bag would be utterly worthless on an wet evac-think of a hurt person in the bottom of a canoe on a cold wet day , hypothermia can be rapid-I have seen a 12-13 boy go from normal to a sub 89F temp inside of 10 minutes-very enlightening experience, and I like that peace of mind that it gives me....it is totally experience driven for me. But I love down too-they are terrific on backpacking dessert and mountain trips and wintercamping....My summer synthetic bags compress to a 7" sphere, and they are 32F bags-short models mind you-and they are light-and when I put them into my 20 year old Marmot 0F down bag it is a bomber winter bag system......-40F no tent on a deck and I slept like a rock not a baby I do understand all of the pros and cons and I have my experiences....to each their own....Synthetic or down I choose both but I'll stick with synthetic when the water is soft.

I think under armor is cold-especially in a cool down situation....Like the synthetic-pataguchii, REI MTS, and the new wool products are very warm but will not dry as fast as the synthetics-which I have done under a tarp in a rain storm----TO EACH THEIR OWN. The other thing that I would say is that the tweeking of one's "system" never stops-make notes on trail at home and keep honing your system.....including the repair kit, first aide kit.....fishing box....and such ......food and cooking Group Dynamics and for God's sake share it with as many as you can

LOL!

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