PURPOSE: To enable a composite material to swell in the presence of water or an aqueous solution by comprising a mixture of hydroexpandable powder and thermobonding powder, sandwiched between two solid supports, one of which is partially hydrosoluble.

CONSTITUTION: A composite material 1 formed of two flat solid supports 10 and 11, one 11 at least of which is completely or partially hydrosoluble, bonding together by a mixture 12 of hydroexpandable polymer powder and thermobonding polymer powder, is placed between an external, sheath layer 2 and a core, or an internal sheath layer 3 of a cable. The supports, in particular the partially aqueous supports are consisting of a non-woven fabric, a textile, a paper or a synthetic film and the hydroexpandable polymer is chosen from modified acrylic polymers, grafted starches, polyacrylamides, carboxymethylcellulose and its derivatives. The thermobonding powder is chosen from the thermoplastic polymers capable of bonding two fibrous or solid surfaces together, such as the polyethylenes and polyamides.