Cables and optical fibers are mainly used underground, underwater, or in the air. Therefore, water can penetrate the cable and cause problems if the outer sheath is damaged.
To prevent water from penetrating the cable, a layer of superabsorbent polymer is placed between the outer cable layer and the cable core. Therefore, if there’s damage to the external sheath and water enters, the SAP polymer absorbs any liquid and swells, thereby protecting the cable due to the blocking effect of the gel.
The following diagram illustrates the structure and mechanism for preventing water ingress.
These superabsorbent polymers are pretty different from those used for disposable diapers because they must last several tens of years. They have a much greater capacity to resist biological or other factors of degradation. Polymers based on polyacrylate chemistry have a high water absorption capacity, which reaches up to 400 times their mass in water. An effective formula against saltwater was also developed.