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.
Photo Credit: Alan D. Wilson
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 it's ability to trap air. To measure fill power, one ounce of down is compressed in a small glass cyclinder. 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.
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 $350 and weighs 29 oz. Contrast this bag with the Mountain Hardware Merced 15, another highly rated 15 degree goose down bag with a fill rating of 600. It retails for $314, but weighs 51 oz., a 22 oz. difference.
As a rule of thumb, it is usually worth paying a premium for a sleeping bag or a quilt that contains high fill down if you plan on keeping it for many years. However, unless 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.
Related posts:
