What is the desirable properties of an insulation material?

Insulation materials have the desirable properties are as follows:

1. Very fine dielectric strength such as of mica (upto 80 kV/mm at 25⁰C).

2. Volume and surface resistivity equivalent to which of sulphur.

3. Good mechanical strength as which of steel.

4. Very high crushing resistance (as which of granite).

5. Simple of machining.

6. Good fire proofing qualities (as which of silica).

7. This must have very high chemical inertness.

8. This must have good water proofing qualities same to that of paraffin wax.