In fiber optic cable, a gel-like substance called "filler gel" or "optic cable filling compound" is often used. The specific composition of the gel can vary depending on the manufacturer and the optic cable's intended application. The gel is typically made from a combination of polymers, such as petroleum jelly, mineral oil, or silicone compounds. These materials offer a good balance of properties, including moisture resistance, thermal stability, and mechanical protection for the optical fiber.