Testing Down Quality: Down Percentage
Down % is measured by hand picking. Every single piece in a very small sample of down is separated into categories such as down, down fibre, downy feathers, feathers etc etc. Each category is then accurately weighed (we used to work with scales accurate to one thousandth of a gram) and the down content then stated as percentages: 90/10, 80/20, etc. As a higher first figure means a higher down content, this test is often quoted as another promotional statement about down quality (even 100% has been claimed). Unfortunately that is often the main value of the test — a promotional statement — because there is no single international standard by which these figures are produced and the degree of possible variation makes them virtually meaningless.
As an example, you would be wrong in assuming that a '90/10' down always contains 90% down. In the first place what classification of the word down is being used — how much does it include of the middle categories between pure down and pure feather? There are guidelines but no accepted worldwide standard, and differences in classification exist. And secondly, measuring down content is a long, tiresome business, only applied to the tiniest fraction of the down being processed: it gives a rough guide only and the figures are unlikely to be checked.
In the end the only way for a manufacturer to be sure of what he is saying is to do picking tests himself: and even then he is likely to be spending a lot of time in testing .001% (one part per 100 thousand) of what he uses.
Overall it is better to treat down/feather figures as comparatively unimportant. An experienced manufacturer can tell immediately if there is any increase in the feather content of a down and it will also show up adversely in fillpower testing. After all, if extra feathers improved the fillpower, who would care about the classification of the material?