In reply to OopzISlippedAgain:
I have used it on a Rab Kinder and ME Dew line (300g of down) the Dew line bag is used by my wife and it maintained its loft far longer in damp conditions than my brand new Rab 300g of down bag! If dried and stored correctly it should not affect the loft of the bag.
How ever it'll only slow down the loss of loft when sleeping in damp conditions. After 14 days of bivying in wet alps I am serisouly looking at man made fibres as the both bags lost a lot of loft.