duck down vs goose down

Duck down is cheaper than goose down.

Forgive me I do not know much

Is 700 duck down the same weight and warmth of 700 goose?

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The fill number is the cubic inch number of 1 oz (28.3 g) of down .
So a 550 fill takes up 550 cubic inches and 800 takes up 800 cubic inches, both weighing 1 oz .

700-fill duck down will LOFT the same as 700-fill white goose down. It might be cheaper.

At the 500 to 550-fill levels commonly found with duck down, it is markedly cheaper than goose down. A "fill" rating is a standardized test measuring the ability of a given amount of insulation to fill (loft) an empty cylinder to a certain degree. Density, feather vs. cluster ratio, and the insulation's ability to prevent moisture absorption all come into play, as I understand it.

The catch is that 750-fill White goose down might perform the same as 550-fill duck down when used in inside your sleeping bag, in the field. It is not a coincidence that such things are perceived as difficult to accurately measure in the lab, methinks.

Edited only for grammatical reasons…