well a quick google showed this..
This is the ability of the down to loft (ie its ability to resist compression) and the higher the Fill Power value the better the quality of the down. To calculate the Fill Power a set weight of down is compressed by a specific weight and the volume it takes up under this condition measured. The actual measure is a minimum that must be attained by the down so the values have a + figure at the end. There are two measures of fill power to be aware of: European and US. We have stated European measures next to our down clothing and sleeping bags, but here are some comparisons to help you: 560+ European equates to 610+ US, 660+ European equates to 725+ US and 750+ European equates to 850+ US.
Although the basic method of measuring fill power is consistent, there is no actual universal standard. Most down products are currently rated according to one of two systems, one European (the Lorch Fill Power standard recommended by the Swiss-based International Down and Feather Laboratory) and one American. Both systems measure fill power in cubic inches. The higher the number (i.e. the greater the volume), the greater the ability to trap air.
500–600 EU (530–640 US) Acceptable quality for mid-market products
600–700 EU (640–745 US) Minimum quality for performance products
700–800 EU (745–850 US) Excellent quality, best performance/price ratio
800+ EU (850+ US) Outstanding quality, limited availability, high price
And finally this from PHD
PHD have expanded the range of downs we use from two to three with the introduction of our exceptional 900 quality down. All three downs, 700, 800 & 900 are European goose downs, the best of their kind, backed by our own almost fifty years of experience in the trade as well as by our own Lorch test machine....
Remember that our figures are based on the standard Lorch test as approved by the International Down and Feather Bureau. These figures are roughly 4% more conservative than US Federal tests, as quoted by some other manufacturers.