Function
A featherbed is a down and feather filled bag that lays on top of the mattress. A duvet is a blanket that covers the sleeper.
Featherbed Advantages
Featherbeds provide extra comfort in conjunction with the mattress by cushioning the body, especially at pressure points like shoulders and hips.
Duvet Advantages
A duvet, in the traditional sense, furnishes the sleeper with a single covering. It takes the place of top sheet, blanket and spread, which simplifies bed-making.
Considerations
Duvets typically have a cover that can be removed for laundering. A fitted sheet covers the featherbed and mattress together.
Featherbed Construction
Featherbeds are constructed with baffles or channels to keep the down and feathers in place and usually have a gusseted side about two inches wide. Featherbeds can contain 5 to 15 percent down and 95 to 85 percent feathers with an outer covering of a high thread-count cotton.
Duvet Construction
The duvet can use baffle or channel construction or it may be quilted to keep the filler in place. The filling is down and feathers, wool, silk, cotton or polyester batting.