CST - Screen is not surrounded with dielectric

Hello all,
In "Cable groups" I am adding a new cable. Insulator outside is defined by PVC material. In Insulator inside I want to define a new material. In creating a new material there is no dielectric material option. Which is shown in the screenshot. I cannot place screen as it need to be surrounded with dielectric (as shown in screenshot).

CST Studio Suite ​​​​​​​