Method and mold for producing air ducts (P) from plastic material, especially soft plastic material, with a hardness of between Shore 5 and Shore 65, of the type comprising a hollow main body (P1) provided with at least one protuberance or nipple (P2) that projects from the exterior wall of the main body (P1), the method comprising the steps of injection-molding at least one nipple (P2) from plastic material inside a first cavity (1) of a mold (M); interconnecting the first cavity (1) with a second cavity (3) arranged in the same mold (M) and located adjacent to said first cavity (1), in order to form a single volume; and blow-molding a hollow body from a moldable plastic-material parison inside the second cavity (3).