This routine calculates the capacitance of a parallel plate capacitor,
neglegting fringing effects. The following are the relative permittivites
and breakdown voltages of some common capacitor materials - source RS.

Material       Relative Permittivity                      Dielectric strength.

PTFE           2.0/2.1 @ 10 Hz to 10 Khz                  >   24 kv/mm.
Nylon 66              ?                                   >   12 kV/mm.