In some applications the umbilicals need to have negative buoyancy, in others neutral and some-times even positive. But there are some characteristics in common:
The umbilicals need to be water tight, robust and long lasting. Most of them have Kevlar, Aramid or Polyester ﬁbers incorporated, in order to achieve high tensile forces at a low weight.
The outer jacket may be of Polyurethane, Silicon or Polyethylene. Multipolar cables are mostly used nowadays, but simple coaxial cables are available as well as single conductor cables.