Fill power is a measurement of how well the down in an item can insulate. Essentially, the amount of fluff and down that is needed to keep you warm. The best quality down does a better job with less down then lower quality down.
Measuring Fill Power
The measurement of fill power is on a scale of up to 900. This number is determined by an experiment in which the down is compressed in a plexiglass cylinder. The larger the number the higher quality in down. For example, 400 is considered the low end of good down, 550-700 are very good down items and as you head up to 900 you are moving into luxury down territory.
Here is what you should look for when judging down products:
Fill Rating – Those items that have good down fill power will have that rating put right on the product. That means you should see a number like 400, 600 or 700. The higher the number, the better. If you don’t see a rating number on a down product, that is likely because it has fallen below the 400 range and is not considered decent quality.
Down in Comforters – You always want to make sure to get a decent fill rating in comforters. Comforters with a lower fill rating are more likely see the down move around and create cold spots, where it is not insulated.
Down in Pillows – While you may think the higher level of fill power in pillows would mean a stiffer pillow that is not true. In pillows you must not only know the fill power of the pillows, but also how much down is in the pillow as it will still take more of a higher quality material to create a firmer pillow.