Fill power measures how fluffy, soft, and warm the down is. By using higher fill power down, Cuddledown comforters will be lighter and softer for the same amount of warmth. A lighter down comforter will drape over you better, move easier when you move, and give you a more comfortable night's sleep.
The fill power test is performed in a laboratory, measuring the ability of down to regain its shape when pressure is released. To calculate fill power, you place an ounce of down in a calibrated tube and apply a pressure weight. When the weight is removed, the down lofts, and you measure the cubic inches it fills in the tube - that's its fill power. This is a test of the down quality in terms of the resilience, durability, and memory of the down. The test results give us a measurement of how warm the down is ounce for ounce. The higher the fill power, the warmer the down.
"Fill power" equals the total number of cubic inches that one ounce of down will fill. Therefore, one ounce of 800 fill power down fills 800 cubic inches of space.
One ounce of 800 fill power down will be warmer than one ounce of 600 fill power down. In order to make a 600 fill power down comforter the same warmth level as a higher fill power comforter, we simply add more ounces of the 600 fill power down. The result is the same warmth level with a slightly heavier weight.
A good quality down will usually have a fill power greater than 550 cubic inches per ounce. Below that level the fill may contain a lot of feathers or damaged down clusters and will not be very good quality.
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