A high-voltage composite insulator is substantially comprised of a rod (2) of synthetic material reinforced with fiber glass, screen forming bodies (3) and connection armatures (4). The outer cylindrical surfaces of the rod (2) of synthetic material reinforced with fiber glass are coded with a first layer (5) of silicon rubber and with a second layer (6) of synthetic plastic grease. The screen forming bodies (3) are crimped on said outer layer of the rod (2) of synthetic material. These screen forming bodies are made of polytetrafluoroethylen. They present in the direction of the longitudinal axis thereof smooth cylindrical bores (7). The diameter of these bores (7) is very slightly smaller than the diameter of the rod (2) covered by said layers. The screen forming bodies (3) supported by the synthetic material rod (2) are heated before their mounting and then set on the rod (2). In order to prevent water or dirt from penetrating inside the screen forming bodies (3) threaded onto the synthetic material rod (2), these bodies are preferably assembled by a tongue and groove joint (9a and 9b).