What is Fill Power?

What is Fill Power?

The term “fill power” is often used in connection to duck & goose down quilts but what does it mean?

Fill power is a measure of the ability for duck & goose down to expand (when tested in ideal conditions). Technically speaking Fill Power refers to the number of cubic inches that one (1) ounce of down will occupy when allowed to reach it’s maximum loft.

For example one (1) ounce of 800 fill power goose down will loft to 800 cubic inches. The higher the fill power the larger the down cluster is. Larger down clusters will loft higher; sleep softer, last longer and sleep warmer!

The larger the down cluster, the higher the fill power. Larger down clusters come from older, larger and more mature birds. The pictures below show the difference between a large (high fill power) down cluster taken from a mature bird and a smaller (low fill power) down cluster from a younger, less mature bird.

Fill powers (based on the IFDB method) typically range from under 400 (low quality duck or goose down) and up to 800+ (premium grade Hungarian goose down).

Quilts made using high quality European down (600+ fill power) are lighter, warmer, fluffier and will last much longer than cheaper ones made using low fill power down (400-500 fill power) sourced from Asian countries where the birds are typically slaughtered at an earlier stage of maturity.

The picture below shows different levels of fill power

The International Feather & Down Bureau (the world largest feather and down authority) recognises two methods for measuring fill power.

These are:

  • IFDB Method – used by Europe, Canada, USA and Australia
  • GB/T Method – used by China and other Asian countries

While the testing methodologies are different and yield different results, a general rule of thumb for converting the GB/T results to a comparable IFDB result is to multiply the result by 40.


If the GB/T result is 15cm fill power, the equivalent IFDB result is 600 fill power (i.e. 15 multiplied by 40)

Duck & goose feathers do not have any ability to expand, and so do not have a fill power rating.

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