What is fill power? Down quality explained simply

If you compare down duvets, sooner or later you will come across the term fill power. It describes how much volume a given amount of down takes up under test conditions. That says a lot about the quality of the filling, but not everything about how warm your duvet is.

What down is

Down is not the same as feathers. It is the fine, fluffy layer beneath the feathers of waterfowl such as geese and ducks, and it protects the birds from cold and wet. Most down grows on the belly, where the birds come into contact with water most often. A down cluster has no hard quill, just many fine filaments. Between them it traps air, and it is this air that insulates.

Valued for centuries

As early as the 14th century, people in Europe slept on feather beds and down pillows, and later down covers were added to sleep under. Good down bedding was often passed down from generation to generation. Durability is still a sign of good quality today.

What fill power measures

Fill power is a measure of volume. A sample of down is placed in a measuring cylinder under a set weight. The space it takes up is then read off. It is stated differently depending on the region:

• In the USA in cuin/oz, cubic inches per ounce. A fill power of 600 cuin means that one ounce of down fills 600 cubic inches.
• In Europe often in cm³/30 g, cubic centimetres per 30 grams of down.

When comparing, make sure both values are given in the same unit.

What the number tells you and what it does not

The higher the fill power, the more volume for the same weight. Down with a high fill power traps more air. So less filling is needed for the same warmth, and the duvet becomes lighter.

But how warm a duvet is does not depend on fill power alone. The amount of filling and the construction also play a part, meaning how the filling is distributed and held in place inside the duvet. A high number on its own does not make the right duvet. Read more in our guide What makes a good duvet?.

Light or medium-warm

Also think about how you sleep and how warm your bedroom is. Our down duvet comes in two warmth levels: Light for anyone who gets warm quickly at night, and Medium-warm, balanced and comfortable all year round. It is filled with fine European down, made in Switzerland and DOWNPASS and OEKO-TEX® STANDARD 100 certified.

If you prefer to sleep without down, the synthetic duvet is the alternative, with a filling of fine polyester. You will find all our down products in our down bedding collection.

How to keep the fill power

Give your duvet a quick shake every day and air it regularly. Avoid fabric softener when washing, as it coats the fibres and the down lofts less. How to wash and dry your duvet at home is explained in our article Washing your duvet and pillows at home.