At real camping stores there is a liquid additive for cleaning down vests, coats , pants, and sleeping bags. The additive is there to help the down fluff back up! the use of tennis shoes is highly recommended.
For winter backpacking, I have 2 zip together Hollo Fill II -5 degree bags, they get the same treatment. These two good bags zipped together with the wife and I in them and inside a tent have been used to 20 below Zero F with very favorable results. Some people prefer a cloth liner, but I found clean long johns (and clean wool socks!) to work better! Hers is a Large Long (4.5 pounds of fill), mine is a extra-large Long LEFT HANDED (5.0 pounds of fill) by Slumberjack. They were 2/3 thirds the price of down, but still insulate when damp (Down won't), and 20% heavier than down, but I believe in the "Prepare for the Worst" kind of equipment. I store them in large laundry bags inside a large coolers, so they stay fluffy! (and the mice can't find them!)
Around 1988, my wife loaned an light weight summer bag to a college age girl from church for a weekend backpacking trip. Mush-for-brains returned the bag covered in K-1 fuel!, and no apology. I had the bag cleaned and forbid the loaning of ANYTHING to her again. (Our Church did yearly camp outs, I had gear to outfit about 6 additional families and loaned it freely, it was always returned in clean and usable condition) 2 other guys had extra equipment to loan out, but they wouldn't loan equipment to people who mistreated it either!
Ivan