For years, sleeping bag science has been relatively simple. If you want to save money: get a sleeping bag with synthetic fill; if you want to save weight: get a bag with a down fill. And wet synthetic fill does keep you warm, whereas wet down gives does not.
Excuse my while I blow your mind.
Sierra Designs has created DriDown. Dridown is a hydrophobic membranous finish which bolsters Sierra Designs down to heights never before reached. DriDown absorbs water at a rate 10x slower than normal down, giving its insulating and loft qualities a seemingly untouchable edge over any other down insulator. It doesn't take a genius to figure out why Outside Magazine embraced the Sierra Designs Zissou 0 as its top winter camping sleeping bag.
At just three pounds one ounce (1.4 kg), the Zissou's snuggly warmth rating of zero degrees, paired with its state-of-the-art DriDown technology, make the Sierra Designs Zissou the premier winter camping sleeping bag. The Sierra Designs Zissou 0, equipped with DriDown, made the Outside Magazine 2012-2013 Winter Buyer's Guide with ease.
See Sierra Design's DriDown video: here