a method is disclosed for producing seamless tubular articles such as plumbing traps and the like which have an arcuate portion along their tubular axis . mating die members are provided which , when clamped together , define a mold cavity configured to the external shape of the article to be formed . a tubular parison of heated thermoplastic resin is extruded and has an outside diameter less than the outside diameter of the article . while still pliable , the parison is bent to the general shape of the article and the die members are clamped about it with at least the bent portion inside the mold cavity . a blow molding duct is introduced into the parison and pressurized fluid is introduced through the duct to expand the parison outwardly into contact with the surfaces of the mold cavity . when the plastic has cooled sufficiently to rigidify , the die members are separated and the molded article is stripped from the mold . apparatus for performing the method is also disclosed .