Background story: I put my duvet (synthetic filling) into a washing machine, and the machine was unable to spin-dry it. My mom told me: "It's because it is full of air".
I was not satisfied with the answer. So: Why is it problem for a washing machine to spin-dry a synthetic duvet? From my point of view, the only important factor is the momentum of inertia, that depends only on the weight and distribution of the weight.
I do not think that the momentum can be significantly higher for a single duvet than for a large lot of casual clothes.