What Is Down Fill Power?

Down, like any insulating material, 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. The more fill power a down product has, the thicker the layer of air inside it. Thus, a higher fill power means better insulation. Higher quality down will have greater fill power, meaning less material is required to provide the same level of insulation. In essence, 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 value, down is washed and dried, 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.

The Lorch-cylinder measures down fill power

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 given in millimetres per 30 grams. We made a table to help you navigate the different ways of measuring fill power:

Fill Power Conversion Table
mm/30gram 125 150 155 160 170 180 190 200
in³/oz (cuin) 500 600 618 635 675 725 760 800

How Much Fill Power Do You Need?

To determine the right amount of fill power for your duvet, close your eyes and 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 relative, but nonetheless important for discerning consumers.

Multiple cylinders with different kinds of down and different fill power

Maintaining Your Down

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 creates airiness 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, read more about the differences between a goose down duvet and a duck down duvet.

Down Duvet Buyer's Guide

Choose your duvet in 4 simple steps

  1. Duvet size: Which duvet size do I need?
  2. Tog: Choose the right tog
  3. Fill power: What is Fill Power?
  4. Ticking: Good down belongs in a good ticking

Compare all down duvets by duvet price, size, season, brand, fill power, ticking and down.

Do you have any questions? Feel free to ask us!
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