Floatable flexible electric and/or optical line

A floatable flexible line comprising a plurality of conductors and a flexible one-piece casing having an extrudable cross-section shape and comprising an inner cylindrical wall and an outer cylindrical wall with a plurality of radial walls extending therebetween, said walls being impermeable to air and liquid, said inner cylindrical wall surrounding said conductors, said walls defining a plurality of air chambers extending longitudinally of said line for providing buoyancy thereto, said casing being constructed of an extrudable thermoplastic rubber having a density of less than 1 kg/dm.sup.3 for supplementing the buoyancy of said line.