Down Fill Power Explained
The fill power of down is a standardized measure of the down used for making that product. Down insulation is an amazing natural product used to insulate the body from outside cold. It is used in jackets, sleeping bags, comforters and other items. The fill power of down is an industry standard used to measure the quality of the down. However, the fill power alone will not tell you how warm the product will be.
Fill power is a standard way of measuring the quality of down feathers. What this measure is actually looking at is the amount of space (volume) a single ounce (or about 30 grams) of down takes up when compressed with a certain weight. The USA and Europe use slightly different measurements. The end result is a measure of how much space an ounce of down takes up.
This is not a measurement of warmth or durability of the down. All it is a measure of is the volume that down takes up. However, the way down insulation works is by trading warm air in-between the down feathers. The more space there is between feathers, the more warm air down is able to trap. So there is a correlation between the warmth of the down filling an the fill power. The fluffier the down, the more heat it can hold.
An 800 fill power down sleeping bag will not always be warmer than a 650 fill power sleeping bag. The other aspect in warmth is how much down is used. For example, an 800 fill power down sleeping bag which uses one pound of down will not be warmer than a 650 fill power down sleeping bag which uses three pounds of down fill. Though pound-for-pound the 800 fill bag will be warmer, because the 650 fill bag uses more down overall, it will be warmer.
When choosing a down product be sure to look at the fill power, but also at other aspects such as how much down is used altogether. This will give a clearer picture of the true warmth of the down product.
Fill power differences originate with the age of the bird from which the down was collected. Mature birds have larger individual down feathers, creating a fluffier, higher quality down with a higher fill power. Younger birds have not developed such high quality feathers, leading to lower fill power.
Down fill power ratings are especially important in sleeping bags, jackets and other outdoor products. This is because high quality high fill down will be able to provide a warmer product while weighing less. The weight of a sleeping bag, jacket, etc. can be the difference between an enjoyable hike and a grueling backbreaking hike. Remember, higher fill power means less weight for the same amount of warmth.
High fill power also means that the product is more compressible. The larger amounts of air pockets between the down mean that the product can be compressed into a smaller space. Again, this is of great importance when looking for high quality outdoor gear. The less space your sleeping bag takes up, the smaller a backpack you will need.
For comforters, a high fill power means that the comforter will weigh less and hold more heat. If you like light-weight comforters, than a high fill down comforter may be the right item for you.