The "warm when wet" myth about synthetic bags is just that, IMHO, a myth. I found from bitter experience that a wet synthetic bag is just as cold as a wet down bag. Admittedly, the synthetic is a bit easier to dry out. Whatever kind of bag you have, the most important thing you can do is keep it--and your insulating clothing--dry. That means some kind of waterproof container (not a stuff sack, which isn't) in your pack--waterproof pack liner, plastic bag or dry bag.

Most of us on this board find that down--high quality down--the kind that cost lots of $$$--will outlast several synthetic bags if properly cared for. It therefore ultimately pays for itself, if you can save up enough cash for it. Admittedly, for a lot of people, that's the big IF. Down most certainly can be washed, if you're careful with it! My dog, by the way, is never allowed on my sleeping bag--doggie claws and a $330 down bag with a lightweight shell just don't go together, even if the dog is clean and sweet-smelling! If my dog gets into something smelly (fortunately, he hasn't yet), he's going to sleep out in the vestibule, or maybe out under a tree (depends on how smelly)!