Because the duvet is an animal protein fiber, higher than cotton (botanical cellulose) insulation, and down spherical fiber dense with tens of thousands of triangular thin pores, can shrink and expand with the temperature change, produce temperature-regulating function, can absorb the human body emitting flowing heat, isolated from the outside cold air invasion. Responsible for saying that down products are best not to be placed in a compressed space, at least not for a long time to place in the compressed space. Because it will destroy the structure of the down itself, resulting in not fluffy, not warm, and there will be odors and shorten the life of the hidden danger. As the structure is destroyed, bacteria breed and produce odors. Crushed fiber structure, there is no way to return to fluffy, so it is not warm.
Not only the duvet, usually fluffy things (down jacket, down sleeping bags, etc.) is best not long-term compression, only when the travel needs to temporarily compress, otherwise it will affect the fluffy degree, resulting in a decrease in heat preservation performance.