DUCT

A duct includes a circumferential wall. At least part of the circumferential wall is a fibrous portion that includes fibers. The fibrous portion includes a breathable inner layer located on an inner circumferential side in the circumferential wall and an outer layer located on an outer circumferential side of the inner layer in the circumferential wall. The outer layer is less breathable than the inner layer. A boundary between the inner layer and the outer layer is breathable.