The ballasts and buoys according to the present invention for ducts, with closure devices, have the same design and the same closure devices, and differ only by the material they contain. The ballasts designed to anchor underwater or underground duct lines have a body (1) made of flexible or rigid materials and can contain dense cores (14) and (19) encapsulated inside the body, or be compact (15) and (20) and be entirely made of dense materials or composites. The buoys, which are intended to keep duct lines on the surface of water, have a body (1) made of flexible or rigid materials and can be hollow and contain light cores (14) and (19) or be compact (15) and (20) and be entirely made of low-density materials. Both the ballasts and the buoys according to the present invention can be flexible, hinged or divided into two parts, with closure devices with a flange (5), screws (10) and nuts (11), or straight closures (8) with angular guides.
