Capacitive

What is a DK value (dielectric constant)?
The DK value (εr) describes the electrical properties of substances and represents an important parameter in applications of the capacitive measuring principle. With this technique, the DK value must be stable in order to make measurement possible. It determines the size of the capacity change, which is then measured and evaluated in the electronics.
The DK value list can be found here:
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Implementation of partly insulated/fully insulated capacitive electrodes
Partly insulated measuring probes serve exclusively for measuring electrically nonconductive media. If the medium to be measured is electrically conductive, a fully insulated measuring probe is used.

A good rule of thumb is:

 DK value < 5 = partly insulated measuring probe
 DK value > 5 = fully insulated measuring probe