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Down Fill Power Ratings: The Low Down on Goose Down


If you are on the market to purchase a new sleeping bag, quilt, or a down filled parka, it’s helpful to understand why high fill goose down is better than lower quality goose down. But first, it’s helpful to understand why goose down is such an effective cold weather insulator.

Goose Down Ratings

Goose down consists of fluffy filaments that are a lot like human hair. A single ounce of average quality down contains about 2 million of these filaments which interlock to keep warm air in and cold air out. This layer is very springy so you can scrunch it up by compressing it, but it will spring back into shape almost immediately.

Fill power measures the lofting power of goose down which is its ability to trap air. To measure fill power, one ounce of down is compressed in a small glass cylinder. When the weight is removed, the down’s ability to spring back can be measured.  Down with a higher fill power rating is more resilient to compression, lofts better, and can trap more air. Besides being warmer, this also means that sleeping bags or parkas with a higher fill ratings require less insulation by weight to provide the same level of warmth than an item made with lower quality down.

For example, sleeping bags or quilts with a fill rating of 800-900 will provide an outstanding level of warmth and are preferred by backpackers who want a warm but very lightweight piece of gear. Sleeping bags with fill ratings of 600-700 are considered very good, 500-550 is considered good, and 400-450 is considered medium quality.

Western Mountaineering Sleeping Bag - 850 fill power goose down
Western Mountaineering Sleeping Bag – 850 fill power goose down

However, goose down with a fill rating greater than 700 is quite expensive. Most commercially available goose down only has a fill rating of 400-550 because it comes from immature geese that have been raised for human consumption. Higher quality goose down with a fill rating in the 550 to 850 range down is collected from geese that are allowed to reach their full maturity and are specially bred for this purpose. This is far more expensive process resulting in higher consumer prices.

To put this in perspective, the sleeping bag shown above is a Western Mountaineering Ultralite 20 with a goose down fill rating of 850. It retails for about $485 and weighs 29 oz. Contrast this bag with the Kelty Cosmic Down 21 sleeping bag, another highly rated 20 degree goose down bag with a fill rating of 550. It retails for about $170, but weighs 41 ounces, a difference of 12 ounces or 40% heavier.

As a rule of thumb, it is usually worth paying a premium for a sleeping bag or a quilt that contains high fill power down if you plan on keeping it for many years.  However, unless it’s a question of survival, you can probably get by with a lower fill rating for down filled jackets and parkas which you’re less likely to keep for a long time.

Additional Resources

For more information about the warmth of goose down, see:

REI Expert Advice: Sleeping Bags for Backpacking

REI Expert Advice: How to Choose Insulated Outerwear

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  1. Not sure who wrote this but 'quilts' do not contain down. 'Comforters' are filled with down.

    • Before you criticize people’s use of language, you might want to consult a dictionary:

      quilt (kwlt)
      1. A coverlet or blanket made of two layers of fabric with a layer of cotton, wool, feathers, or down in between, all stitched firmly together, usually in a decorative crisscross design.
      2. A thick protective cover similar to or suggestive of a quilt.

    • He is talking about backpacking quilts which are basically sleeping bags without a back or zipper.

  2. Sorry, down quilts are all the rage in the ultralight backpacking community. You can't expect people to call them comforters, now. :-)

  3. Excellent information about goose down fill rating. I think it's worth paying more to get a lighter sleeping bag that will last longer. I have used my goose bag for over 25 years and I could not go back to a synthetic bag.

  4. Quilt calling blankies "comforters"! It spreads sheets of confusion, forcing me down to take cover.

  5. Eric Sahar Pinkham

    Where can I buy good quality down? My down bag has lost a lot of it’s fill.
    Thank you.

  6. I have two sleeping bags, one with 600 down and one with 850. I’ve noticed that the bag with 850 down seems to be much more sensitive to moisture. In humid conditions, my evaporating body moisture will condense in the down, sometimes causing a dramatic loss in loft overnight. The 600 fill seems to do this a lot less… the “lower quality” down is more robust in real world conditions.

    Anyone else notice this?

    Sierra Designs is now producing down items with a hydrophobic treatment on the down that is supposed to make it water resistant. I’d like to see a review of that technology.

  7. I absolutely agree with Jarra. Above about 500 fill, I find down becomes increasingly sensitive to moisture and pressure, even though it’s warmer for the weight under ideal conditions. This means if I’m going somewhere cold and dry and where weight/bulk really counts, I’ll take a higher quality down bag (and a really good underpad, i.e. at least R-insulation value 6). Otherwise I prefer the less compressible mid-quality down for its maintained loft after multiple days use. Note that geese themselves operate with both down and feathers– the feathers resist compression and provide waterproofing to make a perfect system.

  8. I am attempting to modify an old sleeping bag. my plan is to open it at the seams, remove the synthetic filling, replace it with 900 fill power down from ThruHIker. my questions is how much of the down will i have to use to obtain a temp rating of 30-35 degrees? should i use all 900 fill? or a blend? I also plan on putting most of the down in the upper portion of the bag to offset the loss by compression and get more “bang for my Buck” with the down.
    thanks for any info

    • Contact Thru-hiker and he’ll tell you what to do.

    • @jay: be careful– synthetic bags are usually structured very differently from down ones, and you may find it impossible to remove the insulation without taking apart almost every seam in the bag. Synthetic insulation usually comes as a sheet that gets sewn into the bag shingle fashion. The insulation forms the structure of the bag (there are no baffles). Only down bags have fabric tubes or columns that one can “inject” new down into.

  9. Wikipedia: The 700+ down fill comes from a small number of birds kept for breeding purposes throughout the year. These geese molt naturally in the spring. While their down is loose it is collected by hand. It is very rare and, of course, expensive.

  10. This may be a stupid question, but how can a bag with 550 & one with 850 both be rated 20 degrees. Doesn’t one have more down and should be warmer?

    • The number (or fill power) refers more to the quality of the down, not the actual quantity of it. A higher number (fill power) will result in less down being needed to achieve the same insulation rating. A 20 degree bag with 550 fill power may weigh (for example only. Not a true weight of the bag) 5lbs and a 20 degree bag with 800 fill power may weigh 3lbs.

      In theory, you could have 2 different 550 fill power bags, with different temperature ratings, depending on the actual volume of the 550 fill power down that is used.

  11. The 55o fill power bag should have more down fill by weight since it is less insulating and lower quality down.

  12. I still don’t understand this rating as it seems incomplete to me. While 850 down is understandably warmer than 600 fill, if I buy a jacket in 850 fill power could it be less warm than a 600 jacket? Doesn’t it have everything to do with how much (weight) of a given fill is used? Should it be determined by both amount and power? I seldom find the weight or amount of fill on descriptions, only the fill power. I’m concerned with two two things, overall weight of a garment and how warm is it compared to the overall weight. How do I determine this?

    • Yes. You need to know the weight of the down and the fill power. Even then you may not know how warm the jacket is, because the down is distributed throughout the coat unevenly. To find the absolute weight of the down in the coat, contact the manufacturer if they don’t publish the spec. Most don’t.

    • You are absolutely correct.
      all the sites that rate “the best this or that” by trumtpiting the fill power almost always leave out the fill weight amount.

      It is impossible to compare these items without that information.

      Major makers used to list the fill weights. I know that the North Face formally listed this information.
      However when they became a fashion maker that information stopped appearing.
      Look at the company “Feathered Friends” from Seattle. They list the fill weights

      Who cares if it has 900 fill power when it is as thin as a tissue.

      Give me a nice “chubby’ 600 fill power item

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