Inlet duct for internal combustion engine

An inlet duct for an internal combustion engine, the inlet duct comprising a tubular main body formed by a compression-molded fibrous molded body, wherein

• the main body includes an alternate layout region in which an air-impermeable high-compression portion and an air-permeable low-compression portion that is compression-molded at a lower compressibility than a compressibility of the high-compression portion are alternately laid out in an axial direction of the main body,
• the alternate layout region is divided into an upstream region and a downstream region of a central position in an axial direction of the inlet duct in a flow direction of intake air, and
• the alternate layout region is configured such that an arbitrary pair of points at an equal distance in the axial direction to the central position in the upstream region and the downstream region include only points that are both located in the low-compression portions and points one of which is located in the low-compression portion and the other one of which is located in the high-compression portion.