In reply to gear boy:
> it shouldnt lose that much down, ever
Indeed, and if it has, it may not be worth re-filling if it's only going to leak again...
The other possibilities are that it's been stored damp, and the down had degraded and no longer lofts as well, or it's had
massive amounts of use, and been repeatedly stuffed and re-stuffed into a tiny stuff sack so that the down clusters have fractured.
Or it may just have been crap down in the first place...
As for losing efficiency, well, if you lose down, the item will just be less warm. It will still work, but it won't be as warm as a new jacket of the same type; it will be about as warm as a different jacket with about the same amount of down filling in it...