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Down Fill
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Down Fill
Down fill utilizes the fine inner feathers from geese. It provides very good warmth for its weight and it also very compressible. Down is used as insulation in everything from sleeping bags and quilts, to clothing, to sleeping pads.
Fill Power
Often times manufacturers will state the "fill power" of the down used in the product. Fill power (FP) is a measure of how much volume (in cubic inches) one ounce of down will occupy. For example, one ounce of 800 FP down will expand to fill approximately 800 cubic inches. This means that to fill a given volume, the amount of down required decreases as the FP of the down increases. So in the case of sleeping bags, a bag using 800 FP will weigh less than a bag with the identical volume of 650 FP down.
Down to Feather Ratio
While fill power is the most often listed feature of down, quality is also indicated by the ratio of pure down to coarse feathers. The higher the percentage of pure down, the better and more expensive the fill. A ratio of 90 percent down to 10 percent feathers or higher is common in good quality fill.
Pros/Cons
Traditionally down bags weighed much less than their synthetic counterparts. As synthetic technologies have progressed, however, the gap has narrowed considerably. For summer weight bags the difference in weight is not as dramatic but as temperature rating increases, down's weight advantage becomes more apparent.
Down bags also have the ability to compress smaller than comparable synthetic bags. However the topic of how much to compress insulation is a hotly debated one. There are many differing opinions on how much compressing any form of insulation speeds its degradation, though it is generally agreed that down is more durable over repeated compression cycles.
The biggest drawback of down is its notoriety for losing its insulating properties when it gets wet. While any insulation will lose some of its insulating potential when wet, down is reported to more fully "collapse" under the wetest conditions than some common synthetics. Thus the topic of whether to use down or synthetic for wet climates is a hot button issue. Many people that choose down bags say that extra caution needed to keep a sleeping bag dry is a small sacrifice for the weight savings.
Finally, down is more expensive than synthetic, though it can be debated that the down lasts longer and that over the long run it is a better investment.
