Inlet duct for internal combustion engine

An inlet duct for an internal combustion engine comprising a duct member made of a compression molded fiber material, wherein

• the duct member includes a main body and a first end portion and a second end portion provided on opposite sides in an axial direction of the main body,
• the main body includes a first half cylinder body and a second half cylinder body,
• each of the first half cylinder body and the second half cylinder body includes joining portions at opposite ends in a circumferential direction of the main body,
• the joining portions of the first half cylinder body and the joining portions of the second half cylinder body are joined together,
• the main body includes multiple high-compression portions and at least one low-compression portion, which is made through compression molding at a compression ratio lower than a compression ratio of the multiple high-compression portions, the multiple high-compression portions and the at least one low-compression portion being provided in the main body other than the joining portions of the first half cylinder body and the joining portions of the second half cylinder body,
• the multiple high-compression portions are spaced apart from each other both in the circumferential direction and the axial direction of the main body, and
• the at least one low-compression portion comprises a line portion that continuously extends between the first end portion and the second end portion throughout a length in the axial direction of the main body.