|The differences between duck and goose feather inners|
The primary difference between goose and duck, as far as bedding is concerned, is the size of the down cluster. In geese, the down cluster is generally larger and the barbules are spaced farther allowing the cluster to trap air more efficiently than a smaller duck cluster and giving thereby cluster a higher rate of insulation compared to it's weight. Goose down duvets therefore usually have better insulation or a higher tog value for the same fill weight than their duck down counterparts. Both, however, are far better insulating materials than synthetic alternatives.
There are also different types of goose and duck and one rule of thumb is that the colder the climate the birds frequent, the larger the down clusters will be and the more insulation you will get per gram of that filling.