A process for manufacturing a plastic hollow body including extruding a molten plastic parison through a die. At least one longitudinal cut is made in the parison. The parison is introduced into a mold comprising two cavities. The hollow body is molded by conforming the parison to the mold cavities. The die includes a passage for the molten plastic which gradually modifies the shape of the parison so that it is substantially flattened on exiting.