Shopping for Goose Down? Here’s What to Know About ‘Down Fill Power’

Have you run across the term “down fill power” while shopping for sleeping bags, puffer jackets, or a duvet? These numbers range from 450 to 900, and sometimes above. Generally—but not always—the higher that number, the better the warmth-to-weight ratio. But what does fill power actually measure?

To measure fill power, companies perform a lab test to measure the fluffiness of down. The technical test is how many cubic inches of loft come from one ounce of down. A container is filled with one ounce of down insulation, then a weight is placed on top. After one minute of being compressed by the weight, the volume of down under the weight is measured. The important thing to keep in mind is that fill power is a measure of the quality of the down, not the quantity. Higher fill power means larger down clusters, and ...