Since down and feathers are natural materials they undergo a certain natural ageing process. In the course of time the filling gradually desiccates and you will find an increasing number of broken and damaged down and feathers. You can slow down the process by proper care (fluff up the duvet or pillow every day and air them regularly), but you cannot stop it.
If your duvet is not worn out, you should have it cleaned to remove residue such as sweat. Besides, worn out filling components, in particular broken down and feathers are picked out and replaced by new material.
If your duvet has been used for a very long time, it will hardly be worthwhile to have it cleaned. You should rather consider to purchase a new one.
It is generally advised to replace a pillow after 5 years of use at the latest. You should purchase a new duvet after 8 to 10 years.
Further information at :
Quelle
Verband der Deutschen Daunen- und Federnindustrie e.V.
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