A good duvet must
Read the label and various seals.
Particularly concerning the filling, which you cannot normally see, the label offers valuable help, It specifies the colour and origin of the feathers/down, whether it is new or reprocessed material, from which fowl species (goose, duck) the feathers/down come from and also the percentage of feathers and down in the blend. Being aware of this composition is especially important, since down not only has a higher heat insulation capacity and a lighter weight than feathers, but is also significantly more expensive.
As a result, the percentage of down in a duvet, for instance, is one of the most important criteria in determining its value - if the down content is high, the duvet is generally more valuable and expensive than one with a lower percentage of down (and thus a higher feather content).
Pillows require a filling material that is capable of offering long-term support ('cushioning') to the head and possibly the upper part of the body during sleep. This is why many people prefer down-feather blends.
Another popular option are multi-chamber pillows, where separate chambers are filled with down or feathers. Here, the feathers assume the supporting function whilst the down filling creates a pleasant sleeping environment.