What is Down Fill Power?

Down thumb

If you’ve been shopping for a down jacket to keep you warm this winter, you’ve probably noticed they are labeled 550-fill, 650-fill and 800-fill. You may wonder, what is down fill and what is the difference between 650-fill down and 800-fill down?

The down fill power number found on down jackets and down sleeping bags doesn’t refer to the amount of down in the product like many people think. Actually, it refers to the quality of the down used in the product. Fill power is a measurement of the loft of the down. When it comes to down insulation it is the loft or air caught within the down that creates the warmth. The more loft the warmer that particular down will be in a jacket or sleeping bag.

The number of fill power is the measurement of space that one ounce of down takes up. One ounce of 550-fill power down will take up 550 cubic inches of space. One ounce of 800-fill down will take up 800 cubic inches of space, and so on. Currently the highest rating of down is 900-fill. Goose down of that quality is rare and is therefore more expensive than lower rated down.

So basically, the higher the number of fill power the fluffier the down in the jacket. The fluffier the down the warmer you will feel in the jacket. However, a lower quality down jacket that has more down in it (thicker fill weight) can be warmer than a higher quality down with less down in it (lower fill weight), but in general terms when comparing two similar jackets or sleeping bags, the higher number of down fill power will be the warmer choice.

Down under 550-fill is considered lower quality. Down from 600 to 700-fill is considered high quality and down over 700 is excellent. You’ll pay more for higher quality down but it will be warmer, weigh less and will pack down smaller than lower quality down.

Since it takes less of the higher fill power (fluffier) down to create warmth, a sleeping bag will 800-fill down will weigh less and pack smaller than a sleeping bag at the same temperature rating with 650-fill power down.

Sierra Trading Post offers many down jackets from 800-fill to 650-fill to 550-fill and below.

Hopefully this answers your questions about down fill power and now you can make a wise choice when comparing down jackets, down vests or down sleeping bags.

You may also be interested in:

How to Wash a Down Sleeping Bag
Caring for a Down Sleeping Bag
Tips for Choosing the Right Sleeping Bag
Down vs. Synthetic: A Buying Guide

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Andy Hawbaker
Andy is a hiker, backpacker, snowboarder and outdoor fanatic. When he isn't exploring the Rocky Mountains with his wife and daughters he shares his adventures here on the Sierra SocialHub.

5 comments on “What is Down Fill Power?

  1. Evelin Roof

    A sleeping bag’s temperature rating identifies the lowest temperature at which a bag is intended to keep the average sleeper warm. When a bag is described as a “20 degree bag,” it means that most users should remain comfortable if the air temperature drops no lower than 20°F. These ratings assume that the sleeper is wearing a layer of long underwear and using a sleeping pad under the bag.”-::

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