In this work the dielectric losses of low‐density polyethylene used in submarine telecommunication cables have been measured as a function of pressure (1–1150 bars), temperature (4–32 °C), and frequency (0.3–12 MHz). These results point out that the dissipation factor tan &dgr; and permittivity &egr; of the insulators increase on the sea bottom; for example, for a cable laying at the depth of 5000 m and temperature of 4 °C, these variations are about &Dgr; tan&dgr;=35×10−6, (F=12 MHz), &Dgr;&egr;=5×10−2.