No matter in a shopping mall or on a on line shop like Amazon, even the sleeping bags may indicate the same fill power but have really great difference between their prices.
Generally speaking, you may think that the goose down is no doubt better than duck down. Well, what kind of animal does the down comes from may be a really important reference index a few years before, however, with the fast improvement of technology, duck down has been very close to the goose down in term of the fluffiness, and the feather with the same fill power, whether it is goose down or duck down is equally effective in keeping warm.
Duck down is cheaper after all, way much cheaper than goose down. It’s a common practice in the industry to replace goose down with duck down, even without increasing the fluffiness of duck down. Unless you bring it up for inspection, it’s impossible to tell whether the sleeping bag is filled with duck down or goose down, or whether there’s a great harmony between two.
If you are willing to sacrifice your sleeping bag and insist to find out what exactly it is inside, but don’t want to send it for a inspection, then you’ll need a microscope.
Even you get a microscope, can you distinguish duck down and goose down in the photo below?
I’ll just suggest to choose a duck down from a reliable brand, and take goose down if you have never heard about the brand.