What role does the 'double-sided high-density down bag' mentioned in the padding description play as a detail?

A down bag refers to the invisible pocket fabric inside down clothing that directly holds the feather filling. In padded garments, if the filling is placed directly between the outer fabric and the lining, sharp feathers can easily poke out through weaving gaps or sewing needle holes. To remedy this, applying a down bag involves layering densely woven high-density fabric to enclose the filling.

RE RHEE's MELANGE DUCK DOWN PUFFER BLACK uses duck down filling blended with down 80% and feathers 20%^[1]. While maintaining warmth due to the high down content, the mixture of feathers with stiff quills can cause feather leakage when friction occurs. This jumper is finished by layering high-density down bags on both sides of the filling to reduce the phenomenon of feathers transferring to the surface of the outer fabric or to clothes worn underneath^[2].

Although invisible to the eye, it is a finishing detail that holds the shape and filling in place from the inside so that feather leakage from the garment is reduced and it can be worn for a long time.