Like any insulating material, down provides warmth by creating pockets or layers of air which protect against the cold. The thicker the layer of air, the better the insulation.
We measure the quality of down in “fill power”, a measure of the loft, or “fluffiness”, of a down product. Higher quality down will have greater fill power, meaning less material is required to provide the same level of insulation. In simpler terms, fill power is the warmth-to-weight ratio of down.
Measuring Fill Power
We measure fill power in CUIN, or cubic inches per ounce. To calculate this, down is washed, dried, and then put into a device called a Lorch cylinder. Once inside, a set amount of pressure is applied to the down. At that point, the height of the down is measured and this number determines the down’s fill power.
The fill power of our duvets ranges from 600 CUIN to 800 CUIN for products with the highest quality down.
Down Fill Power Conversion
Fill power is the best quality indicator for down. Most down products in Europe are rated according to the Lorch Fill Power standard recommended by the Swiss-based International Down and Feather Laboratory. UK companies report fill power in cubic inches. In Germany and Austria (where our duvets are manufactured), fill power is measured in millimetres per 30 grams. We made a table to help you navigate the different measurements of fill power:
How Much Fill Power Do You Need?
To determine the right amount of fill power for your duvet, ask yourself how light or heavy your dream duvet feels. If you prefer a very light duvet which is also warm, you need a down duvet with high fill power. If you don’t mind your duvet being heavier, feel free to choose a duvet with lower fill power. Of course, most modern duvets are exceptionally light, so the differences in weight are minimal, but still important for some consumers.
The fill power of down will decrease with time and usage. To counteract this process, regularly hang your duvet outside on a dry day, or in a well-aired room. When down clumps together, shake it loose by hand or put the duvet in a dryer with a dampened (and well-wrung) towel. The warm, moist air will loosen the tufts of down and create air pockets without sacrificing fill power. To read more about how to care for your down duvet and pillows, visit our maintenance page.
If you’re interested to learn more about down, read more about the differences between a goose down duvet and a duck down duvet.